How to use it
- Choose what to solve for: the ending balance by default, or the deposit, return, years or starting amount (then enter a target).
- Enter amounts, rate, years and compounding; More options adds yearly deposit increases and inflation.
- Read the result, the breakdown chart and the yearly schedule, and export CSV for further analysis.
Growth of 10,000 with compound interest
Compounded annually with no further deposits. Both rate and time magnify compounding: at 7%, 20 years gives 3.9× and 30 years 7.6×.
| Annual rate | 5 years | 10 years | 20 years | 30 years |
|---|---|---|---|---|
| 3% | 11,593 | 13,439 | 18,061 | 24,273 |
| 5% | 12,763 | 16,289 | 26,533 | 43,219 |
| 7% | 14,026 | 19,672 | 38,697 | 76,123 |
| 10% | 16,105 | 25,937 | 67,275 | 174,494 |
Effect of compounding frequency
At the same 5% nominal rate, more frequent compounding gives a higher effective rate, though monthly to daily adds little. Compare products by effective annual yield (APY), not the nominal rate (APR).
| Compounding | Effective annual rate |
|---|---|
| Annually | 5.000% |
| Quarterly | 5.095% |
| Monthly | 5.116% |
| Daily | 5.127% |
| Continuously | 5.127% |
Rule of 72: years to double
Divide 72 by the annual growth rate in percent to estimate the years to double. It is most accurate between 6% and 10%.
| Annual rate | Rule of 72 | Exact years |
|---|---|---|
| 2% | 36.0 | 35.00 |
| 4% | 18.0 | 17.67 |
| 6% | 12.0 | 11.90 |
| 8% | 9.0 | 9.01 |
| 10% | 7.2 | 7.27 |
| 12% | 6.0 | 6.12 |
| 15% | 4.8 | 4.96 |
| 20% | 3.6 | 3.80 |
Frequently asked questions
What return should I assume?
Plan with long-run, conservative figures, e.g. 1–2% for money market, 3–4% for bonds, and 6–8% often used for broad equity indices. Returns are not steady, so also check a lower scenario.
How accurate are the results?
Formulas are exact and compounding is simulated period by period, shown to the cent. Real returns fluctuate and banks differ on day counts, tax and fees, so use the results for planning and comparison.