How does compound interest work with regular withdrawals?

When you withdraw money, the principal shrinks but the remaining balance still earns compound interest. The math: each year, the balance grows by (1 + rate), then you subtract the withdrawal. If your rate exceeds the withdrawal percentage, the portfolio grows. If withdrawal exceeds rate, it depletes. Example: $1M at 7% return − $40K/yr withdrawal = balance grows in early years because 7% × $1M = $70K > $40K spending. As portfolio shrinks (if withdrawals are inflation-adjusted), the math tightens.

How long will my $1 million last with $40,000 annual withdrawals?

Under a constant 7% real-rate arithmetic model, a $1M balance and a $40,000 first-year withdrawal may not deplete when the withdrawal is increased with 3% inflation, but that result is only a fixed-rate scenario. Historical sequence, fees, taxes, changing withdrawals and the chosen horizon can produce a different outcome. Enter the assumptions in the calculator instead of treating a single duration as a retirement guarantee.

What is the safe withdrawal rate for compound interest with withdrawals?

The Trinity paper and later withdrawal studies tested specific historical periods, portfolio mixes, withdrawal rules and horizons. Their results describe those assumptions rather than a universal safe rate. For a longer retirement, compare several starting rates, flexible spending rules, fees, taxes and sequences in the calculator; do not treat 3%, 3.5% or 4% as a recommendation without matching the method.

How do I calculate compound interest with both deposits and withdrawals?

Two-phase formula. Accumulation: A1 = (P × (1+r)^t) + (PMT × [((1+r)^t − 1) / r]). Decumulation: each year, balance = balance × (1+r) − withdrawal. To see if the portfolio lasts N years, iterate the decumulation formula N times. Snowballr's calculator runs this automatically — set positive monthly contribution during accumulation phase and toggle to negative for withdrawal phase.

What is the 4% rule for retirement withdrawals?

The classic 4% rule starts with 4% of the initial portfolio in year one, then adjusts that dollar amount for inflation. Historical backtests report high, but assumption-dependent, success rates over 30-year periods; they are not a guarantee. Example: a $1M portfolio starts at $40,000, then $41,200 in year two at 3% inflation. The 25× rule is the inverse: multiply annual expenses by 25 to get a starting target.

Does sequence of returns risk affect compound interest with withdrawals?

Yes. Two portfolios with the same average return can have different outcomes when losses occur early or late relative to withdrawals. Test a lower return, a larger early withdrawal and a flexible-spending case; a deterministic calculator cannot reproduce every market sequence. For personalized Social Security estimates, use the official SSA estimator.

Can I model lump-sum withdrawals (not just annual)?

Yes. Model the accumulation phase, subtract the lump sum at its stated date, then continue with the same or revised assumptions. The effect depends on the amount, timing, rate, fees, taxes and remaining horizon; run both the withdrawal and no-withdrawal cases rather than relying on a generic lost-growth figure.

Free · Two-phase: accumulation + decumulation · 4% rule built-in

Compound interest calculator with deposits and withdrawals

Model both phases of retirement: accumulation (deposits + growth) and decumulation (withdrawals + growth). Set a positive monthly contribution for saving and a negative amount for withdrawal. Historical 4% research is shown as context, with assumptions kept visible.

6 worked withdrawal scenarios

How long your portfolio lasts depends on three things: starting balance, withdrawal amount (as % of balance), and real return. These six scenarios cover the most common cases:

Scenario	Portfolio	Withdrawal	Rate	Lasts
Trinity 4% rule: $1M / $40K Historical-study context; portfolio mix and withdrawal rules differ	$1,000,000	$40,000/yr (4%)	7% real illustration	Run a stated horizon
Lean FIRE: $625K / $25K Arithmetic 4% starting-withdrawal case	$625,000	$25,000/yr (4%)	7% real	Run a stated horizon
Conservative: $1.25M / $40K (3.2%) Lower-rate scenario; not a universal safe rate	$1,250,000	$40,000/yr (3.2%)	5% real illustration	Compare 40/50-year cases
Aggressive: $500K / $30K (6%) Higher starting withdrawal; sequence risk matters	$500,000	$30,000/yr (6%)	7% real illustration	Test depletion under assumptions
Fat FIRE: $2.5M / $100K Same arithmetic withdrawal percentage; taxes and fees excluded	$2,500,000	$100,000/yr (4%)	7% real illustration	Run a stated horizon
Late starter: $400K / $30K (7.5%) Higher withdrawal percentage; add verified income separately	$400,000	$30,000/yr (7.5%)	6% real illustration	Test the bridge horizon

The math: two-phase compound interest

Phase 1 — Accumulation (you're contributing):

A = P × (1 + r/n)^(nt) + PMT × [((1+r/n)^(nt) − 1) / (r/n)]

Where P = starting balance, PMT = monthly contribution, r = annual rate, n = compounding periods/year, t = years. PMT is positive during accumulation.

Phase 2 — Decumulation (you're withdrawing):

balance_n+1 = balance_n × (1 + r) − withdrawal_n

Each year, the balance compounds first, then withdrawal is subtracted. For inflation-adjusted withdrawals: withdrawal_n+1 = withdrawal_n × (1 + inflation). A rate comparison alone cannot establish survivability; sequence, timing, fees, taxes and the horizon also matter.

How to interpret a withdrawal projection

They use average returns. Real markets are volatile. A "7% average" can mean +30%, -20%, +10% — sequence matters more than average for retirees.
They ignore inflation on withdrawals. A $40K withdrawal today is $72K equivalent in 20 years at 3% inflation. Most calculators assume fixed-dollar withdrawals.
They ignore taxes. A 401(k) withdrawal at 22% bracket means $40K withdrawn = $31K spendable.
They ignore other income unless you enter it. Use a personalized Social Security estimate or pension statement and model its timing separately; do not substitute a generic benefit amount.

Sources: Cooley/Hubbard/Walz 1998 (Trinity Study), Bengen 1994 (historical withdrawal-rate research), Robert Shiller historical data, Karsten Jeske Safe Withdrawal Rate Series and the official Social Security estimator. Historical results are context, not a guarantee. Last updated: 2026-10-03.

By Snowballr Research Team

Last reviewed October 3, 2026Fact-checked against primary sourcesEditorial standards

Coverage: Compound interest · Retirement · FIRE · Debt payoff · Mortgages · Fraud prevention

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