Doubling time at common rates
| Return | Rule of 72 | Exact |
|---|---|---|
| 4% | 18.0 years | 17.7 years |
| 6% | 12.0 years | 11.9 years |
| 7.1% | 10.1 years | 10.1 years |
| 8% | 9.0 years | 9.0 years |
| 10% | 7.2 years | 7.3 years |
| 12% | 6.0 years | 6.1 years |
| 15% | 4.8 years | 5.0 years |
At PPF's 7.1%, money doubles in about 10.1 years; at 12%, in about 6. The rule also works in reverse for inflation: at 6% inflation, prices double in about 12 years.
Questions people ask
What is the rule of 72?
Divide 72 by the yearly return to estimate how many years it takes for money to double. At 8%, 72 ÷ 8 = 9 years.
How accurate is it?
It is very close for returns between about 6% and 12%. For very high or very low rates, use the exact figure this calculator shows.
Method and sources
Exact years to double = ln 2 ÷ ln(1 + rate); to triple = ln 3 ÷ ln(1 + rate). Rule of 72 = 72 ÷ rate. Assumes yearly compounding. How we calculate.
Last reviewed 22 Oct 2026 by the WealthFeedz team.