Rule of 72 Calculator
The fastest mental shortcut in finance: how many years until your money doubles? Edit either number — the other updates instantly.
At a 7% annual return, your money doubles in about 10.3 years — that's the Rule of 72 (72 ÷ 7 ≈ 10.3). The rule is a quick mental shortcut: divide 72 by your expected annual return to estimate how many years it takes to double your money, or divide 72 by your target doubling time to find the return you need. It's most accurate for returns between about 5% and 12%. Edit either number below to explore the relationship instantly.
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Type in either field — the Rule of 72 links them: years × rate ≈ 72.
Rule of 72 estimate: 10.3 years
To double in 10 years, you'd need about 7.2% per year.
| Annual return | Rule of 72 | Exact |
|---|---|---|
| 4% | 18.0 years | 17.7 years |
| 5% | 14.4 years | 14.2 years |
| 6% | 12.0 years | 11.9 years |
| 7% | 10.3 years | 10.2 years |
| 8% | 9.0 years | 9.0 years |
| 10% | 7.2 years | 7.3 years |
| 12% | 6.0 years | 6.1 years |
How the Rule of 72 works
The rule
To estimate how long it takes money to double at a given annual return, divide 72 by the return (as a percentage):
Example: at 7% return, 72 ÷ 7 ≈ 10.3 years. Flipped the other way: to double in 10 years you need about 72 ÷ 10 = 7.2% per year.
The exact math
The rule is an approximation of the true formula, which comes from solving (1 + r)n = 2 for n:
where r is the annual return and n is the number of years. The Rule of 72 stays accurate to within a few percent for returns between roughly 4% and 15%.
Educational purposes only. Not financial advice. The rule assumes a constant return and ignores taxes, fees and volatility. See the methodology and disclaimer.
Rule of 72, explained
What is the Rule of 72?
Why 72 and not 70?
Is the Rule of 72 exact?
ln(2) ÷ ln(1 + r). For returns between roughly 4% and 15%, the rule of 72 is accurate to within a few percent.