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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 the saving phase, negative for the withdrawal phase. Includes the Trinity Study 4% rule reference.
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 Original Trinity Study assumption — 50/50 stocks/bonds | $1,000,000 | $40,000/yr (4%) | 7% real | Indefinite (96% success at 30 yrs) |
Lean FIRE: $625K / $25K Frugal early retiree, low-cost area | $625,000 | $25,000/yr (4%) | 7% real | 30+ years |
Conservative: $1.25M / $40K (3.2%) Karsten Jeske safe rate for 50-yr horizons | $1,250,000 | $40,000/yr (3.2%) | 5% real | 50+ years |
Aggressive: $500K / $30K (6%) Risky — Trinity says ~57% success at 30 yrs | $500,000 | $30,000/yr (6%) | 7% real | ~22 years |
Fat FIRE: $2.5M / $100K Same 4% rule scales linearly | $2,500,000 | $100,000/yr (4%) | 7% real | Indefinite |
Late starter: $400K / $30K (7.5%) Need Social Security to bridge longevity gap | $400,000 | $30,000/yr (7.5%) | 6% real | ~17 years |
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). The portfolio survives if real_return > withdrawal_rate, generally.
Why most calculators get this wrong
- 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 Social Security. $20-40K/yr SS income reduces the portfolio drawdown burden significantly after age 67.
Sources: Cooley/Hubbard/Walz 1998 (Trinity Study), Bengen 1994 (4% rule origin), Robert Shiller historical data, Karsten Jeske Safe Withdrawal Rate Series. Last updated: 2026-06-01.