Rule of 72 Calculator
Find how long it takes money to double at a given return, or the return you need to double it in a set time.
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Years to Double
- Exact (yearly compounding)
- Continuous compounding
- Rule of 72 error
- $10,000 becomes
- Rule of 69.3
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| Name | Rate | Rule of 72 | Exact | Remove |
|---|
The Rule of 72
Divide 72 by the annual interest rate (as a whole number) to estimate how many years it takes money to double. It works because ln(2) ≈ 0.693, and 72 is close to 69.3 while dividing evenly by many common rates.
Years to double ≈ 72 ÷ rate Rate needed ≈ 72 ÷ years
Exact (yearly compounding): years = ln(multiple) ÷ ln(1 + rate)
The rule of 69.3 is exact for continuous compounding; 72 is closest for yearly compounding around 8%. To triple, use about 114; to quadruple, 144.
Worked Example
Rule of 72 vs. Exact
| Rate | 72 ÷ Rate | Exact Years |
|---|
Tips
The same rule works in reverse for inflation: at 3% inflation, prices double in about 24 years. It's a mental shortcut; use the compound interest calculator for exact figures with contributions.