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Financial glossary

Plain-English definitions of every term used across our calculators and guides — with concrete examples.

123 terms
12b-1 Fee
A marketing and distribution fee included inside some mutual funds' expense ratios, up to 1% annually. Mostly disappearing but still common in legacy 401(k) plans.
Example: A 0.25% 12b-1 fee on $100K = $250/year that goes to the broker who sold you the fund.
From guide Expense Ratios: The Hidden 25% Tax on Your Returns [{YEAR}]
25× Rule
The corollary to the 4% rule: your retirement portfolio target is 25 times your annual expenses.
Example: Spending $50,000 per year requires a $1,250,000 portfolio to retire safely.
From guide How Much Do You Need to Retire? The 25× Rule Explained [{YEAR}]
4% Rule
A retirement withdrawal guideline stating that withdrawing 4% of your portfolio in year one (then adjusting for inflation) historically sustained a 30-year retirement.
Example: A $1,000,000 portfolio supports $40,000 in year-one withdrawals, rising with inflation each year.
From guide How Much Do You Need to Retire? The 25× Rule Explained [{YEAR}]
4% safe withdrawal rate
The maximum percentage of a portfolio that can be withdrawn annually (adjusted for inflation) for 30 years with a high probability of not running out. From the Trinity Study (1998).
From guide The 25× rule explained — your FI number and how to actually hit it
401(k)
An employer-sponsored retirement account that lets employees contribute pre-tax dollars (or post-tax in a Roth 401(k)), often with an employer match.
Example: Contributing $10,000 to a traditional 401(k) reduces your current taxable income by $10,000.
From guide How to Choose Between a 401(k) and a Roth IRA: Complete {YEAR} Guide
529 Plan
A state-sponsored tax-advantaged investment account for qualified education expenses. Earnings grow tax-free; qualified withdrawals are tax-free.
Example: $10,000/year for 18 years at 7% in a 529 grows to $336,000 with no federal tax on growth.
From guide 529 college savings plans: how they work
Account Owner vs Beneficiary
The owner controls the account and chooses the beneficiary (usually a child). The owner can change the beneficiary or use funds for themselves with tax penalty.
Example: If your first child does not need all the funds, change the beneficiary to a sibling, niece, or even yourself.
From guide 529 college savings plans: how they work
Amortization
The schedule by which a loan is paid down, with each payment split between interest (front-loaded) and principal (back-loaded).
Example: On a $300,000 30-year loan at 6%, year-one payments are ~83% interest; by year 25, they're ~83% principal.
From guide 15-Year vs 30-Year Mortgage: Save $248K Interest? Math [{YEAR}]
Annual Percentage Rate (APR)
The yearly interest rate charged on borrowed money, expressed as a percentage. Higher APR debts cost more in interest each month.
Example: A $10,000 balance at 18% APR accrues $150/month in interest before any payment is applied to principal.
From guide Snowball Method Explained ({YEAR}): 5 Steps to Pay Off Debt Fast
Annual Percentage Yield (APY)
The actual annual return after accounting for the effect of compounding. APY is always equal to or greater than the stated nominal rate (APR).
Example: A savings account advertising 5% APR with daily compounding has an APY of 5.13%.
From guide The Beginner's Guide to Compound Interest: How Money Grows Itself
Annual rate
The expected average annualized rate of return — should be a long-term expectation, not last year's number.
From guide How to Use a Compound Interest Calculator (5 Common Mistakes)
APR (Annual Percentage Rate)
The simple yearly interest rate before compounding is applied. Used on loans (legally required) but less useful for comparing savings accounts than APY.
Example: Two HYSAs advertised at "5.00% APR" with different compounding frequencies actually yield slightly different real returns. Always compare APY to APY.
From guide Daily Compound Interest Formula ({YEAR}): $10K at 5% = $10,513 in 1 Year
APY (Annual Percentage Yield)
The effective annual rate of return after accounting for compounding. For daily compounding, APY is always slightly higher than the stated APR.
Example: A 5.00% APR with daily compounding produces a 5.127% APY — that 0.127% is the compounding bonus.
From guide Daily Compound Interest Formula ({YEAR}): $10K at 5% = $10,513 in 1 Year
Asset Allocation
The mix of asset classes (stocks, bonds, cash) in a portfolio, calibrated to balance risk and return for the investor's timeline.
Example: A common starting point: 110 minus your age = stock percentage. At 30, that's 80% stocks, 20% bonds.
From guide How to Invest $10,000 in {YEAR}: $10K → $217K Playbook
Asset Location
Choosing which account type holds which asset class to minimize tax drag — bonds and REITs in tax-deferred accounts, broad index funds in Roth, tax-loss-harvestable assets in taxable brokerage.
Example: Putting a $30K bond allocation in your 401(k) instead of taxable saves ~$200/year in ordinary-income tax on the interest.
From guide How to Invest $100,000 in {YEAR}: $100K → $761K in 30 Yrs (Step-by-Step)
Assets Under Management (AUM) Fee
A fee charged by financial advisors, typically 0.50–1.50% of portfolio value annually, on top of the underlying fund expense ratios.
Example: A 1% AUM advisor on a $500K portfolio holding 0.50% funds creates a 1.50% total annual drag — about 30% of long-run returns gone.
From guide Expense Ratios: The Hidden 25% Tax on Your Returns [{YEAR}]
Back-loaded growth
The pattern where most of the growth in a long-term compound investment occurs in the final years rather than spread evenly over time.
From guide Compound Interest by Decade: $500/mo = $87K (10yr) → $1.5M (40yr)
Backdoor Roth IRA
A legal workaround for high earners above the Roth income limit: contribute non-deductible dollars to a traditional IRA, then immediately convert to Roth. Avoids the income phase-out.
Example: A single filer earning $200,000 (above the Roth limit) contributes $7,000 to a traditional IRA, then converts the same week to Roth — same end result as a direct Roth contribution.
From guide How to Choose Between a 401(k) and a Roth IRA: Complete {YEAR} Guide
Balance Transfer Card
A credit card that lets you move existing credit card debt onto a new card with a 0% intro APR period (typically 12–21 months), in exchange for a 3–5% transfer fee.
Example: Moving $10,000 in credit card debt to a 21-month 0% balance transfer card with a 3% fee costs $300 upfront but saves ~$2,500 in interest if paid off in 21 months.
From guide Personal Loan vs Balance Transfer ({YEAR}): Which Saves More?
Behavioral Finance
The field studying how psychology affects financial decisions. The snowball method explicitly trades mathematical efficiency for behavioral stickiness, validated by 2016 Northwestern Kellogg research.
Example: Gal & McShane (2012) found small-balance wins increased the probability of debt-free completion — the academic basis for preferring snowball over avalanche for most consumers.
From guide Snowball Method Explained ({YEAR}): 5 Steps to Pay Off Debt Fast
Bond Tent
A glidepath where bond allocation rises in the 5–10 years before retirement, peaks at retirement, then declines through early retirement as sequence risk fades.
Example: A 60/40 portfolio at age 60 shifts to 50/50 at retirement (65), then back to 70/30 by age 75 — protecting the "retirement red zone."
From guide Sequence of Returns Risk: Why Early Losses Wreck Retirees [{YEAR}]
Catch-Up Contribution
An extra contribution amount the IRS allows for people aged 50+ to help boost retirement savings later in their career.
Example: A 55-year-old can contribute an extra $7,500 to a 401(k) on top of the regular $23,500 limit, for a total of $31,000.
From guide {YEAR} 401(k), IRA & HSA Limits: $23.5K / $7K / $4.4K (Full Table)
CD (Certificate of Deposit)
A time deposit at a bank or credit union that pays a fixed APY for a fixed term (3 months to 5 years), with an early-withdrawal penalty if you break the lock.
Example: A 12-month CD at 5.10% APY on $10,000 pays exactly $510 of interest at maturity, guaranteed.
From guide CD vs Savings Account ({YEAR}): Which Earns More on $10K?
Closed-form formula
A direct mathematical expression for a calculation, requiring no iteration. Compound interest has a closed-form formula: A = P(1 + r/n)^(nt).
From guide Compound Interest Calculators Compared: Spreadsheet vs Web vs App
Compound Interest
Interest calculated on both the original principal and the accumulated interest from previous periods, causing balances to grow exponentially over time rather than linearly.
Example: $10,000 at 8% compounded annually grows to $21,589 in 10 years vs $18,000 with simple interest — a $3,589 difference from compounding alone.
From guide The Beginner's Guide to Compound Interest: How Money Grows Itself
Compounding Frequency
How often interest is calculated and added to the principal — annually, monthly, daily, or continuously. More frequent compounding produces slightly more growth, but the effect is marginal beyond monthly.
Example: $10,000 at 8% for 30 years: annual = $100,627; monthly = $108,453; daily = $109,121. Monthly captures 99.4% of the benefit vs daily.
From guide The Power of Compound Interest: $100 → $1.5M Examples [{YEAR}]
Compounding Period
How often interest is calculated and added to the principal — annually, monthly, daily, or continuously. More frequent compounding produces a slightly higher effective return at the same nominal rate.
Example: 6% compounded monthly produces an effective annual yield of 6.17%; compounded daily, 6.18%.
From guide The Beginner's Guide to Compound Interest: How Money Grows Itself
Contribution Limit
The maximum amount the IRS allows you to contribute to a specific tax-advantaged account in a given calendar year. Set annually by the IRS and adjusted for inflation in most years.
Example: The {YEAR} 401(k) employee deferral limit is $23,500; contributions above that are not tax-deductible and may trigger 6% excise tax.
From guide {YEAR} 401(k), IRA & HSA Limits: $23.5K / $7K / $4.4K (Full Table)
Credit Freeze
A free request to credit bureaus to block new accounts from being opened in your name. Stronger than a fraud alert.
Example: Freezing your file at Equifax, Experian, and TransUnion takes ~10 minutes online.
From guide Identity theft: what to do if it happens to you
CSRS (Civil Service Retirement System)
The older federal retirement system for employees hired before 1987. Larger defined-benefit pension, no Social Security from federal service.
Example: A CSRS employee with 30 years of service receives ~56% of their high-3 salary as pension.
From guide Federal employee retirement: FERS, CSRS, and TSP
Daily Compounding
Interest calculated and added to the balance every day, so each day's interest is computed on a slightly larger balance than the day before.
Example: A $10,000 HYSA at 5% APR compounded daily earns about $1.37 per day initially, rising slightly each day as the balance grows.
From guide Daily Compound Interest Formula ({YEAR}): $10K at 5% = $10,513 in 1 Year
Debt Avalanche Method
A debt payoff strategy where you pay off debts from highest interest rate to lowest, minimizing total interest paid over the life of the debts.
Example: A 24% APR credit card is paid before a 6% student loan, even if the credit card has a larger balance.
From guide Snowball Method Explained ({YEAR}): 5 Steps to Pay Off Debt Fast
Debt Free Date
The month and year a payoff plan reaches zero balance across all debts. The two strategies typically produce different debt-free dates for the same starting portfolio.
Example: With four debts and $300 extra/month, snowball may finish in 38 months while avalanche finishes in 36 — same money, different ordering.
From guide Snowball Method Explained ({YEAR}): 5 Steps to Pay Off Debt Fast
Debt Snowball Method
A debt payoff strategy where you pay off debts from smallest balance to largest, ignoring interest rates, to build psychological momentum from quick wins.
Example: With debts of $500, $3,000, and $12,000, you attack the $500 first regardless of which has the highest APR.
From guide Snowball Method Explained ({YEAR}): 5 Steps to Pay Off Debt Fast
Diversification
Spreading investments across many assets to reduce the impact of any single one performing poorly.
Example: Owning the S&P 500 instead of one stock means a single bankruptcy costs you ~0.2%, not 100%.
From guide Investing 101 for Beginners: Where to Start in {YEAR}
Dollar Cost Averaging (DCA)
An investment strategy where you invest a fixed amount of money at regular intervals regardless of market price, smoothing out the cost basis over time.
Example: Investing $500 per month into an index fund every month for 12 months, regardless of whether the market is up or down.
From guide Lump Sum vs DCA: Vanguard Study Says Lump Sum Wins 66% [{YEAR}]
Dollar-Cost Averaging (DCA)
Investing a fixed amount on a regular schedule regardless of price. Reduces timing risk but historically underperforms lump-sum investing about 2 out of 3 years.
Example: Splitting $10,000 into $1,667/month for 6 months instead of investing it all on day one.
From guide How to Invest $10,000 in {YEAR}: $10K → $217K Playbook
Doubling period
The number of years it takes an investment to double in value at a given rate. Calculated by the Rule of 72 (72 ÷ rate).
Example: At 8% annual return, money doubles every 9 years.
From guide Compound Interest by Decade: $500/mo = $87K (10yr) → $1.5M (40yr)
Early Withdrawal Penalty (EWP)
The interest forfeited if you cash out a CD before maturity. Typical scale: 3 months of interest on CDs under 12 months, 6 months on 1–4 year CDs, 12 months on 5-year CDs.
Example: Breaking a $25,000 1-year CD at 5% after 6 months forfeits ~$312 of the $625 earned, leaving you $313 of net interest.
From guide CD vs Savings Account ({YEAR}): Which Earns More on $10K?
Effective Annual Rate (EAR)
The actual annual return after accounting for compounding within the year. For monthly compounding at 8% APR, the EAR is 8.30%.
Example: 8% APR compounded monthly = 8.30% EAR. Two products at "8% APR" with different compounding frequencies will have slightly different EARs.
From guide How to Calculate Monthly Compound Interest: $500/mo = $452K
Effective tax rate
The blended rate paid on investment returns, accounting for the mix of qualified dividends, ordinary dividends, short-term gains, long-term gains, and interest.
From guide Tax-Adjusted Investment Projections: Real After-Tax Returns
Eighth Wonder of the World
An idiomatic English phrase used to describe something extraordinary that exceeds the famous Seven Wonders of the Ancient World. Applied metaphorically to compound interest because of its non-intuitive exponential power.
Example: Other things called the "eighth wonder" in popular culture: Niagara Falls, the Taj Mahal, the New York skyline, the Panama Canal.
From guide Did Einstein Say Compound Interest Is the 8th Wonder? Fact-Check
Emergency Fund
Cash reserved in a liquid, low-risk account to cover unexpected expenses or income loss without resorting to debt.
Example: A household with $4,000 monthly expenses targeting 6 months needs $24,000 in a HYSA.
From guide Emergency Fund: How Much Do You Need? 3 vs 6 Months [{YEAR}]
Employer Match
A contribution your employer makes to your 401(k) based on what you contribute, typically up to a percentage of your salary.
Example: A 100% match up to 5% of salary on a $80,000 income is a free $4,000 per year.
From guide How to Choose Between a 401(k) and a Roth IRA: Complete {YEAR} Guide
Exact doubling time
The mathematically true doubling time at a continuous rate r: t = ln(2) / ln(1 + r). The Rule of 72 is an approximation of this formula.
Example: At 8% (r = 0.08): t = ln(2) / ln(1.08) ≈ 0.6931 / 0.0770 ≈ 9.006 years.
From guide Rule of 72 Explained ({YEAR}): Formula, Math Proof, Full Rate Table
Expense Ratio
The annual fee charged by a mutual fund or ETF, expressed as a percentage of assets. Deducted automatically, it compounds against you the same way returns compound for you.
Example: A 1% expense ratio on $500,000 over 30 years costs ~$200,000 in lost final wealth vs a 0.04% index fund.
From guide The Power of Compound Interest: $100 → $1.5M Examples [{YEAR}]
FDIC Insurance
U.S. government insurance that protects bank deposits up to $250,000 per depositor, per bank, per ownership category, in case the bank fails.
Example: A married couple at one bank has $500,000 of joint coverage ($250k each) plus more across individual accounts.
From guide Best HYSA Rates {YEAR}: 5.00% APY Top Picks (Verified Weekly)
Federal Funds Rate
The benchmark interest rate set by the Federal Reserve that banks charge each other for overnight lending. HYSA rates loosely track this.
Example: When the Fed Funds Rate sits at 4.5%, top HYSAs typically pay 4.0-5.0% APY.
From guide Best HYSA Rates {YEAR}: 5.00% APY Top Picks (Verified Weekly)
FERS (Federal Employees Retirement System)
The retirement system covering federal employees hired since 1987. Includes Social Security, a small defined-benefit pension, and the TSP.
Example: A FERS employee retiring at 62 with 30 years of service receives roughly 30% of their high-3 salary as pension, plus Social Security and TSP withdrawals.
From guide Federal employee retirement: FERS, CSRS, and TSP
FI number
Financial Independence number — the portfolio size at which work becomes optional because investments cover annual expenses indefinitely.
From guide The 25× rule explained — your FI number and how to actually hit it
FIRE (Financial Independence, Retire Early)
A movement focused on aggressive saving and investing to reach financial independence — typically 25× annual expenses — well before traditional retirement age.
Example: Saving 50% of a $80,000 income can reach FI in roughly 17 years, vs 40+ years at a 10% rate.
From guide How Much Do You Need to Retire? The 25× Rule Explained [{YEAR}]
Fraud Alert
A notice on your credit file warning lenders to verify your identity before opening new accounts. Lasts 1 year (or 7 with a police report).
Example: A fraud alert is weaker than a freeze but easier to remove temporarily for legitimate applications.
From guide Identity theft: what to do if it happens to you
Future Value of Annuity
The accumulated value of a series of equal periodic payments at a given interest rate after a specified time. Used to model monthly contributions to retirement accounts.
Example: FV = PMT × [(1 + r/n)^(n×t) − 1] / (r/n). $500/mo × annuity factor at 8%/30yr = $745K.
From guide How to Calculate Monthly Compound Interest: $500/mo = $452K
Guaranteed return
A return achieved with certainty, like the interest rate avoided by paying off a debt. A 22% APR credit card offers a 22% guaranteed return when paid off.
From guide Debt Snowball vs Compound Interest: Which Comes First?
Hardware Security Key
A physical USB or NFC device (YubiKey, Google Titan) that cryptographically signs login challenges, making 2FA bypass effectively impossible.
Example: A YubiKey 5C NFC costs ~$55 and protects Vanguard, Fidelity, Coinbase, Google, and password manager logins simultaneously.
From guide Personal Data Security {YEAR}: Stop 99% of Account Takeovers in 1 Hour
High-Deductible Health Plan (HDHP)
A health insurance plan with deductibles of $1,650+ (single) or $3,300+ (family) for {YEAR}, required to qualify for HSA contributions.
Example: Many employer plans labeled HSA-eligible meet HDHP criteria automatically.
From guide HSA Strategy {YEAR}: Triple-Tax-Free Account → $487K at Retirement
High-Yield Savings Account (HYSA)
An FDIC-insured savings account, typically offered by online banks, paying interest rates significantly higher than the national savings average.
Example: A 4.5% APY HYSA on a $20,000 emergency fund pays ~$900/year in interest, vs ~$90 at a brick-and-mortar bank.
From guide Best HYSA Rates {YEAR}: 5.00% APY Top Picks (Verified Weekly)
Home Equity
The portion of the home you actually own — market value minus remaining mortgage balance. Builds slowly under 30-year amortization, quickly under 15-year.
Example: A $400,000 home with a $320,000 mortgage has $80,000 of equity. After 10 years on a 15-year vs 30-year, equity differs by roughly $80,000.
From guide 15-Year vs 30-Year Mortgage: Save $248K Interest? Math [{YEAR}]
HSA (Health Savings Account)
A triple-tax-advantaged account paired with a high-deductible health plan: tax-deductible contributions, tax-free growth, and tax-free withdrawals for qualified medical expenses.
Example: Maxing an HSA at $4,400/year for 30 years at 8% with no withdrawals grows to ~$487,000.
From guide {YEAR} 401(k), IRA & HSA Limits: $23.5K / $7K / $4.4K (Full Table)
HYSA (High-Yield Savings Account)
An online savings account paying a variable APY that floats with the Fed funds rate, with no lockup and full FDIC insurance up to $250K.
Example: In 2026, top HYSAs pay 4.4–5.0% APY with same-day mobile transfers and no minimum balance.
From guide CD vs Savings Account ({YEAR}): Which Earns More on $10K?
Income-Driven Repayment (IDR)
Federal student loan repayment plans that cap monthly payments at a percentage of discretionary income, with forgiveness of remaining balance after 20–25 years.
Example: A SAVE-plan borrower earning $50,000 might pay ~$200/mo regardless of total balance.
From guide Pay Off Student Loans or Invest? Under 5% Invest, Over 7% Pay ({YEAR})
Index Fund
A mutual fund or ETF that passively tracks a market index like the S&P 500, holding the same securities in the same proportions as the index.
Example: Vanguard's VOO tracks the S&P 500 with a 0.03% expense ratio — $3 per year per $10,000 invested.
From guide Investing 101 for Beginners: Where to Start in {YEAR}
Inflation
The general rise in prices over time, reducing the purchasing power of each dollar.
Example: $1,000 in 2003 had the same purchasing power as roughly $1,650 in 2023.
From guide Real vs Nominal Returns: The Inflation Gotcha for Retirement
Initial amount
The starting balance you already have invested, deposited as a single lump sum at the beginning of the period.
From guide How to Use a Compound Interest Calculator (5 Common Mistakes)
Intro APR Cliff
The moment a 0% intro APR period ends and the card's regular APR (typically 19–28%) applies to the remaining balance.
Example: If you transfer $10,000 to a 21-month 0% card and only pay $400/month, you still owe $1,600 when the 0% period ends — and that $1,600 starts accruing at the regular 24% APR.
From guide Personal Loan vs Balance Transfer ({YEAR}): Which Saves More?
IRS Identity Protection PIN (IP PIN)
A 6-digit number from the IRS that prevents anyone else from filing a tax return using your SSN.
Example: Once enrolled, you must include your IP PIN on every tax return; the IRS rejects returns without it.
From guide Identity theft: what to do if it happens to you
Liquidity
How quickly an asset can be converted to cash without losing significant value.
Example: A HYSA is fully liquid (same-day transfer); a 401(k) is illiquid (10% penalty + taxes before 59½).
From guide Emergency Fund: How Much Do You Need? 3 vs 6 Months [{YEAR}]
Lump sum
A single one-time investment with no further contributions, allowed to compound undisturbed.
From guide Compound Interest Examples: 6 Real Scenarios ($100/mo → $700K)
Lump Sum Investing
Investing the entire available amount in one transaction rather than spreading it across multiple deposits.
Example: Receiving a $50,000 inheritance and investing all $50,000 into an index fund on the same day.
From guide Lump Sum vs DCA: Vanguard Study Says Lump Sum Wins 66% [{YEAR}]
MAGI (Modified Adjusted Gross Income)
Your AGI with certain deductions added back. The IRS uses MAGI to determine eligibility for Roth IRA contributions and their phase-out range.
Example: A single filer with MAGI of $155,000 in 2026 is in the Roth IRA phase-out ($150K–$165K) — partial contribution allowed, not the full $7,000.
From guide How to Choose Between a 401(k) and a Roth IRA: Complete {YEAR} Guide
Marginal Tax Bracket
The federal income tax rate applied to your next dollar earned. The U.S. uses a progressive system: 10%, 12%, 22%, 24%, 32%, 35%, 37%. Your bracket determines the value of a traditional 401(k) deduction.
Example: A single filer earning $90,000 in 2026 is in the 22% bracket — every $1,000 contributed to traditional 401(k) saves $220 in current-year tax.
From guide How to Choose Between a 401(k) and a Roth IRA: Complete {YEAR} Guide
Minimum Payment
The smallest amount a lender requires you to pay each billing cycle to keep the account in good standing. On credit cards typically 1–3% of the balance plus interest.
Example: A $5,000 credit card balance at 24% APR with a 2% minimum payment requires roughly $100/month — but at that rate, payoff takes 30+ years.
From guide Snowball Method Explained ({YEAR}): 5 Steps to Pay Off Debt Fast
Monthly Compounding
Interest calculated and added to the balance every month, so each month earns interest on a slightly larger balance than the previous one.
Example: $500/month at 8% annual return compounded monthly grows to $745,180 in 30 years — total contributions are $180,000, the rest is compounding.
From guide How to Calculate Monthly Compound Interest: $500/mo = $452K
Monthly contribution
A recurring deposit added at the end of each month for the duration of the calculation.
From guide How to Use a Compound Interest Calculator (5 Common Mistakes)
Mortgage Prepayment
Paying more than the required monthly mortgage payment, with the extra applied directly to principal to shorten the loan and reduce total interest.
Example: Adding $300/mo to a $300,000 30-year mortgage at 6% saves ~$95,000 in interest and ends the loan ~7 years early.
From guide Pay Off Mortgage Early or Invest? Math by Rate [{YEAR}]
Nominal return
The raw percentage growth of an investment in current dollars, before adjusting for inflation.
From guide Real vs Nominal Returns: The Inflation Gotcha for Retirement
Opportunity Cost
The value of the next-best alternative given up when making a financial decision.
Example: Prepaying a 4% mortgage instead of investing in an index fund returning 8% has a ~4% annual opportunity cost.
From guide Pay Off Mortgage Early or Invest? Math by Rate [{YEAR}]
Password Manager
Software that generates, stores, and auto-fills unique 20+ character passwords for every site, behind a single master password.
Example: 1Password, Bitwarden, and Dashlane are leading options. Bitwarden is free and open-source; 1Password is paid with polished UX.
From guide Personal Data Security {YEAR}: Stop 99% of Account Takeovers in 1 Hour
Personal Loan
An unsecured installment loan with a fixed APR (8–25% typical in 2026), fixed monthly payment, and 2–7 year term. Often used for debt consolidation.
Example: A $10,000 personal loan at 11% APR over 3 years has a fixed $327/month payment, $1,778 in total interest.
From guide Personal Loan vs Balance Transfer ({YEAR}): Which Saves More?
Phase-Out (Roth IRA)
The income range over which the maximum allowed Roth IRA contribution gradually decreases from full to zero. Above the upper bound, no direct Roth contribution is allowed.
Example: A single filer earning $158,000 in {YEAR} is mid-phase-out; their Roth IRA limit is reduced from $7,000 to roughly $3,500.
From guide {YEAR} 401(k), IRA & HSA Limits: $23.5K / $7K / $4.4K (Full Table)
Phishing
A fraudulent attempt to obtain credentials by impersonating a trusted entity via email, text, or phone call. The leading vector for financial account takeover.
Example: An email claiming to be from your bank with a "verify account" link pointing to a near-identical fake site (citi-secure.com vs citi.com).
From guide Personal Data Security {YEAR}: Stop 99% of Account Takeovers in 1 Hour
PITI
The four components of a typical monthly housing payment: Principal, Interest, Taxes (property), Insurance (homeowners). PITI is the right number to budget against, not just P&I.
Example: On a $2,200 P&I payment, adding $400 property tax and $150 insurance brings PITI to $2,750/month.
From guide 15-Year vs 30-Year Mortgage: Save $248K Interest? Math [{YEAR}]
PMI (Private Mortgage Insurance)
Monthly insurance required by lenders when the down payment is less than 20% of the home price. Typically 0.5–1.5% of the loan amount per year.
Example: On a $400,000 home with 10% down ($40,000), PMI of ~1% costs $300/month until equity reaches 20% of the home value.
From guide 15-Year vs 30-Year Mortgage: Save $248K Interest? Math [{YEAR}]
Principal
The original amount of money invested or borrowed before any interest is applied.
Example: If you deposit $5,000 into a savings account, $5,000 is the principal.
From guide The Beginner's Guide to Compound Interest: How Money Grows Itself
Pro-Rata Rule
An IRS rule that requires Backdoor Roth conversions to be treated as a proportional mix of pre-tax and after-tax dollars across all Traditional, SEP, and SIMPLE IRAs.
Example: If you have $60,000 in a pre-tax Traditional IRA and contribute $6,500 after-tax, then convert that $6,500, about 90% of the conversion is taxable because pre-tax balance dominates.
From guide Backdoor Roth IRA Explained: 4 Steps for High Earners [{YEAR}]
Public Service Loan Forgiveness (PSLF)
A U.S. federal program that forgives the remaining balance on Direct Loans after 120 qualifying monthly payments while working full-time for an eligible public-service employer.
Example: A teacher with $80,000 in federal loans paying $300/mo on an income-driven plan can have ~$45,000 forgiven tax-free after 10 years.
From guide Pay Off Student Loans or Invest? Under 5% Invest, Over 7% Pay ({YEAR})
Qualified Education Expenses
Tuition, fees, books, supplies, and room/board for accredited college; up to $10,000/year for K-12 tuition; up to $10,000 lifetime for student loan repayment.
Example: Computers and internet access used for school count; private high school tuition counts up to $10K/year.
From guide 529 college savings plans: how they work
Rate of return
The annualized growth rate of an investment, expressed as a percentage.
Example: The S&P 500 has averaged ~10% nominal / ~7% real over the last century.
From guide Time vs Rate of Return: The Math Nobody Tells You [{YEAR}]
Real Return
The nominal investment return minus the inflation rate — what your money actually grows in purchasing power, not just dollar terms.
Example: A 10% nominal return with 3% inflation is a 7% real return. Over 30 years, that gap turns $1M nominal into ~$412K of real spending power.
From guide The Power of Compound Interest: $100 → $1.5M Examples [{YEAR}]
Receipt-Banking Strategy
The practice of paying current medical expenses out-of-pocket, saving every receipt, and reimbursing yourself from the HSA decades later — turning the HSA into a tax-free growth account.
Example: A $400 receipt from age 35 can be reimbursed at age 65 from an HSA balance that has compounded for 30 years.
From guide HSA Strategy {YEAR}: Triple-Tax-Free Account → $487K at Retirement
Recurring contribution
A fixed monthly or yearly deposit added to an existing investment, also compounding over time.
From guide Compound Interest Examples: 6 Real Scenarios ($100/mo → $700K)
Required Minimum Distribution (RMD)
The minimum amount the IRS forces you to withdraw from a traditional 401(k) or IRA each year starting at age 73. Roth IRAs have no RMDs during the original owner's lifetime.
Example: A 73-year-old with $500,000 in a traditional 401(k) must withdraw ~$18,800 in their first RMD year (using IRS Uniform Lifetime Table divisor of 26.5).
From guide How to Choose Between a 401(k) and a Roth IRA: Complete {YEAR} Guide
Retirement Red Zone
The roughly 10-year window — 5 years before and 5 years after the retirement date — when sequence-of-returns risk is most damaging to long-term portfolio survival.
Example: A 50% drop at age 64 destroys decades of work; the same drop at 80 barely changes the math because most withdrawals have already happened.
From guide Sequence of Returns Risk: Why Early Losses Wreck Retirees [{YEAR}]
Roth Conversion
Moving money from a traditional 401(k) or IRA into a Roth IRA. You pay ordinary income tax on the converted amount now in exchange for tax-free growth and withdrawals later.
Example: Converting $50,000 from traditional to Roth at the 22% bracket costs $11,000 in current-year tax — usually done in low-income years (sabbatical, early retirement).
From guide How to Choose Between a 401(k) and a Roth IRA: Complete {YEAR} Guide
Roth IRA
An individual retirement account funded with after-tax dollars, where qualified withdrawals in retirement are completely tax-free.
Example: A $7,000 Roth IRA contribution at age 30, growing at 8% to age 65, becomes ~$103,000 — all tax-free.
From guide How to Choose Between a 401(k) and a Roth IRA: Complete {YEAR} Guide
Rule of 114
Extension that estimates tripling time. Divide 114 by the rate to find years for money to grow 3×.
Example: At 8%, money triples in 114 ÷ 8 ≈ 14.25 years.
From guide Rule of 72 Explained ({YEAR}): Formula, Math Proof, Full Rate Table
Rule of 144
Extension that estimates quadrupling time. Divide 144 by the rate to find years for money to grow 4×.
Example: At 8%, money quadruples in 144 ÷ 8 = 18 years (two doublings).
From guide Rule of 72 Explained ({YEAR}): Formula, Math Proof, Full Rate Table
Rule of 70
A more accurate variant of the Rule of 72 for low rates (under 5%), using 70 as the numerator instead of 72. Closer to the true ln(2) × 100 ≈ 69.31.
Example: At 3% inflation, prices double every 70 ÷ 3 ≈ 23.3 years (Rule of 72 says 24; exact is 23.45).
From guide Rule of 72 Explained ({YEAR}): Formula, Math Proof, Full Rate Table
Rule of 72
A mental math shortcut that estimates how many years it takes for an investment to double, by dividing 72 by the annual percentage return.
Example: At 8% annual return, money doubles every 9 years (72 ÷ 8 = 9).
From guide Rule of 72 Explained ({YEAR}): Formula, Math Proof, Full Rate Table
Rule of 76
A higher-accuracy variant for rates above ~15%, using 76 as the numerator. Compensates for the curvature of the exact ln(2)/ln(1+r) function at high rates.
Example: At 20% return, money doubles in 76 ÷ 20 = 3.8 years (Rule of 72 says 3.6; exact is 3.80).
From guide Rule of 72 Explained ({YEAR}): Formula, Math Proof, Full Rate Table
Safe Withdrawal Rate
The maximum annual percentage of a retirement portfolio that can be withdrawn without depleting the portfolio over a target retirement length.
Example: The 4% rule — withdrawing 4% of an initial $1M portfolio ($40K) annually, adjusted for inflation, has historically lasted 30+ years.
From guide Sequence of Returns Risk: Why Early Losses Wreck Retirees [{YEAR}]
SEP IRA
Simplified Employee Pension IRA — a retirement account for self-employed people that allows contributions up to 25% of net self-employment income, capped at $69,000 in 2026.
Example: A consultant with $80,000 net income can contribute up to $20,000 to a SEP IRA.
From guide SEP IRA vs Solo 401(k) for self-employed
Sequence of Returns Risk
The risk that the order in which investment returns are received will negatively impact a portfolio when withdrawals are being made, even if the long-term average return is the same.
Example: Two retirees with identical 30-year average returns can end up with $0 vs $2 million depending on whether bad market years hit early or late in retirement.
From guide Sequence of Returns Risk: Why Early Losses Wreck Retirees [{YEAR}]
SIM Swapping
A social-engineering attack where a thief convinces your mobile carrier to port your phone number to their SIM, intercepting SMS-based 2FA codes.
Example: A SIM-swap attacker who has your bank password + intercepted SMS code can drain accounts within minutes. Add a port-out PIN with your carrier to prevent this.
From guide Personal Data Security {YEAR}: Stop 99% of Account Takeovers in 1 Hour
Simple Interest
Interest calculated only on the original principal, with no interest earned on previously accumulated interest.
Example: $10,000 at 8% simple interest earns a flat $800 every year, regardless of duration.
From guide The Power of Compound Interest: $100 → $1.5M Examples [{YEAR}]
SIMPLE IRA
A retirement plan for small businesses with up to 100 employees. Lower contribution limits ($16,000 employee + 3% employer match in 2026) but minimal administration.
Example: Best for businesses with employees who want to provide retirement benefits with minimal cost.
From guide SEP IRA vs Solo 401(k) for self-employed
Solo 401(k)
A 401(k) for self-employed individuals with no full-time employees. Allows both employee deferral ($23,000 in 2026) and employer profit-sharing (up to 25% of net income).
Example: Same $80,000 consultant can contribute $23,000 employee + $20,000 employer = $43,000 total.
From guide SEP IRA vs Solo 401(k) for self-employed
Spreadsheet model
A row-by-row simulation in tools like Excel or Google Sheets, where each row represents one period and the next row depends on the previous.
From guide Compound Interest Calculators Compared: Spreadsheet vs Web vs App
State Tax Exemption
Interest from US Treasury securities (T-bills, T-notes, T-bonds, I-bonds, EE-bonds) is exempt from state and local income tax. Federal tax still applies.
Example: In California (13.3% top rate), a 4.35% T-bill has the same after-tax yield as a ~5.02% CD. The state tax exemption is worth 67 bps.
From guide CD vs Treasury Bills ({YEAR}): When T-Bills Beat 5% CDs
Super Catch-Up (Ages 60-63)
A new SECURE 2.0 provision allowing workers aged 60-63 to make an enhanced 401(k) catch-up contribution of $11,250 (up from $7,500), effective 2025.
Example: A 62-year-old can contribute $23,500 + $11,250 = $34,750 to a 401(k) in {YEAR}.
From guide {YEAR} 401(k), IRA & HSA Limits: $23.5K / $7K / $4.4K (Full Table)
Tax drag
The reduction in compound growth caused by paying taxes on dividends, capital gains, and interest along the way. Typically 0.5-2% of returns per year for taxable accounts.
From guide Tax-Adjusted Investment Projections: Real After-Tax Returns
Tax-Advantaged Account
An account like a 401(k), IRA, or HSA that offers tax benefits — either deferring taxes on contributions or letting growth accumulate tax-free.
Example: Maxing a $7,000 Roth IRA shelters all future gains on that $7,000 from taxes forever.
From guide How to Invest $10,000 in {YEAR}: $10K → $217K Playbook
Tax-deferred
An account (Traditional IRA, 401(k)) where contributions reduce current taxes; growth is untaxed until withdrawal, then taxed as ordinary income.
From guide Tax-Adjusted Investment Projections: Real After-Tax Returns
Tax-free
An account (Roth IRA, Roth 401(k), HSA for medical) where qualified withdrawals incur no tax — including all the growth.
From guide Tax-Adjusted Investment Projections: Real After-Tax Returns
The Einstein Quote
A widely cited but historically unverified attribution: "Compound interest is the eighth wonder of the world. He who understands it, earns it; he who doesn't, pays it."
Example: The quote appears in countless finance books and motivational posts but has no documented Einstein source — the earliest known print appearance is in 1983 ad copy, 28 years after his death.
From guide Did Einstein Say Compound Interest Is the 8th Wonder? Fact-Check
Time horizon
The number of years between when you invest a dollar and when you spend it. Longer horizons compound more.
Example: A 25-year-old investing for retirement at 65 has a 40-year time horizon.
From guide Time vs Rate of Return: The Math Nobody Tells You [{YEAR}]
Total Expense Ratio (TER)
A broader European term covering management fees plus operating costs, often used interchangeably with US expense ratio.
Example: A European UCITS index fund with a 0.07% TER applies the same drag mechanism as a US ETF with a 0.07% expense ratio.
From guide Expense Ratios: The Hidden 25% Tax on Your Returns [{YEAR}]
Total Interest Paid
The cumulative interest cost of a loan over its full term — the most useful single number when comparing mortgage options.
Example: A $300,000 loan at 6% costs ~$348,000 in interest over 30 years vs ~$156,000 over 15 years.
From guide 15-Year vs 30-Year Mortgage: Save $248K Interest? Math [{YEAR}]
Treasury Bill (T-Bill)
A short-term US government debt security (4-, 8-, 13-, 17-, 26-, or 52-week terms) sold at a discount and redeemed at face value. Interest is the difference between purchase and redemption price.
Example: A 52-week T-bill yielding 4.35% bought at $9,565 redeems at $10,000 — a $435 gain over 52 weeks, exempt from state income tax.
From guide CD vs Treasury Bills ({YEAR}): When T-Bills Beat 5% CDs
TreasuryDirect
The US Treasury's own purchase platform (treasurydirect.gov) — no fees, no broker, $100 minimum, direct from the issuer. Alternative: any brokerage (Fidelity, Schwab, Vanguard).
Example: Buying $10,000 of 52-week T-bills on TreasuryDirect takes 5 minutes; the same purchase via a brokerage takes ~2 minutes and clears next-day.
From guide CD vs Treasury Bills ({YEAR}): When T-Bills Beat 5% CDs
Triple Tax Advantage
The unique HSA feature: tax-deductible contributions, tax-free growth, and tax-free withdrawals for qualified medical expenses.
Example: No other US account offers all three; a Roth IRA gives two of three (no deduction); a traditional 401(k) gives two of three (no tax-free withdrawal).
From guide HSA Strategy {YEAR}: Triple-Tax-Free Account → $487K at Retirement
TSP (Thrift Savings Plan)
The federal government's 401(k)-equivalent retirement plan with extremely low expense ratios (0.04-0.05%) and limited fund choices.
Example: TSP's C Fund tracks the S&P 500 at an expense ratio of ~0.05% — among the lowest in the world.
From guide Federal employee retirement: FERS, CSRS, and TSP
Two-Factor Authentication (2FA)
A login process requiring something you know (password) and something you have (phone, hardware key) before granting access. Reduces account takeover risk by 99%+ (Google internal data).
Example: After entering your password, the bank app prompts a 6-digit code from your authenticator app — without that code, the attacker is stopped.
From guide Personal Data Security {YEAR}: Stop 99% of Account Takeovers in 1 Hour