Approximate doubling time: Using the Rule of 72 as a Quick Estimate
Dividing 72 by a positive annual percentage rate gives a rough doubling time. It is convenient for a quick sense check before running a full compound-growth calculation.
Use the Approximate doubling time Calculator to enter your own figures and compare the result with the worked example below.
Approximate doubling time formula
Years to double ≈ 72 ÷ annual rate (%)
Worked example
| Item | Example value |
|---|---|
| Annual interest rate | 8 % |
| Approximate doubling time | 9 |
These are illustrative inputs, not current prices, rates or recommended targets. Where a currency is shown, keep all comparable money amounts in the same currency; conversion examples identify the two sides separately.
How to interpret the result
The shortcut becomes less accurate at extreme rates and does not handle deposits. It is not a promise that an investment will double on schedule.
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Method and further reading
The example follows the FinMathly calculator method. For broader background, see Investor.gov: Introduction to investing. The background resource may use jurisdiction-specific terms; it does not replace the assumptions of this calculator.
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