Rule of 72 Calculator
Years ≈ 72 ÷ annual percent return. Click any i for detail.
Return
Annual return (%)
i
Return
Nominal annual percent. 8 means 8%, not 0.08. |
|---|
How to use this calculator
- Enter an annual percent return.
- Read Rule-of-72 years.
- Compare to ln(2)/ln(1+r) for the exact compound doubling time.
Results explained
Rule of 72 is a mental-math shortcut. Exact doubling time is ln(2) / ln(1 + r) with r as a decimal. Fine for 6–10% sketches; worse at very high or tiny rates.
Quick reference: doubling
72/8 = 9 years. Exact at 8% is about 9.01 years.
| Item | Detail |
|---|---|
| 6% | ~12 years |
| 8% | 9 years |
| 12% | 6 years |
| Compound FV | See compound interest / future value |
Rule of 69.3 is closer for continuous compounding — not used here.
How the estimate is built
years ≈ 72 / r%. Exact = ln(2)/ln(1+r).
Example scenario
8% → Rule of 72 = 9 years.
FAQ
Monthly compounding?
The shortcut ignores intra-year compounding; the exact line assumes annual.
Negative returns?
Doesn’t double.
Rule of 70?
Same idea, slightly different constant.