Compound interest calculator
Type a return rate yourself, or pick a real asset and a historical window — its annual return over that window will feed the projection. Your inputs are saved automatically in this browser.
Real-world scenarios
Click one to load its inputs.Each scenario projects forward at the window’s compound annual return (CAGR). The final number reflects the real outcome of that window, but the chart won’t show the year-by-year volatility along the way.
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One-off lump sums — bonuses, inheritances, sale proceeds — that should land at a specific year. Each lands at year-end and compounds from then on.
Growth over time
Breakdown
| Year | Calendar | Contributed | Gains | Balance |
|---|---|---|---|---|
| 1 | 2026 | $1,200.00 | $123.39 | $2,323.39 |
| 2 | 2027 | $1,200.00 | $229.26 | $3,752.65 |
| 3 | 2028 | $1,200.00 | $343.60 | $5,296.25 |
| 4 | 2029 | $1,200.00 | $467.09 | $6,963.34 |
| 5 | 2030 | $1,200.00 | $600.46 | $8,763.79 |
| 6 | 2031 | $1,200.00 | $744.49 | $10,708.29 |
| 7 | 2032 | $1,200.00 | $900.05 | $12,808.34 |
| 8 | 2033 | $1,200.00 | $1,068.06 | $15,076.39 |
| 9 | 2034 | $1,200.00 | $1,249.50 | $17,525.89 |
| 10 | 2035 | $1,200.00 | $1,445.46 | $20,171.35 |
| 11 | 2036 | $1,200.00 | $1,657.10 | $23,028.45 |
| 12 | 2037 | $1,200.00 | $1,885.66 | $26,114.11 |
| 13 | 2038 | $1,200.00 | $2,132.52 | $29,446.63 |
| 14 | 2039 | $1,200.00 | $2,399.12 | $33,045.75 |
| 15 | 2040 | $1,200.00 | $2,687.05 | $36,932.80 |
| 16 | 2041 | $1,200.00 | $2,998.01 | $41,130.81 |
| 17 | 2042 | $1,200.00 | $3,333.85 | $45,664.67 |
| 18 | 2043 | $1,200.00 | $3,696.56 | $50,561.23 |
| 19 | 2044 | $1,200.00 | $4,088.29 | $55,849.51 |
| 20 | 2045 | $1,200.00 | $4,511.35 | $61,560.86 |
How this works
Compound interest is interest on your interest. Each period your gains earn gains too, so a steady return curves upward instead of growing linearly. The longer the period, the more dramatic the curve — most of the final balance in a long-horizon plot comes from the last handful of years.
Rule of 72: years to double ≈ 72 / annual return %. At 8% money doubles every 9 years; at 10% every ~7.2. The faint dashed lines on the chart mark each predicted doubling (2×, 4×, 8× …) so you can see how the rule lines up with the curve.
Asset prices are hardcoded USD year-end closes (price-only, not total-return), so true dividend-reinvested returns for assets like the S&P 500 or BRK.B are slightly higher than what you see here. Saved scenarios live only in this browser. This calculator is for intuition, not advice.