Rule of 72 Calculator
Estimate how long it takes to double your money, or the return you need to double it, and see how accurate the rule is
Doubling
At 8.00% a year, your money doubles in about
9.00 years
Rule of 72: 72 ÷ 8 · exact answer 9.01 years
Rule of 72
9.00 years
Exact doubling time
9.01 years
ln 2 ÷ ln(1 + rate)
Rule of 70
8.75 years
often used for inflation and GDP
Rule of 69.3
8.66 years
exact for continuous compounding
$10,000 doubling over time
Growing 8.00% a year; each dot is another doubling
How accurate is each rule?
Error in the doubling time as a % of the exact answer; 0% is exact
Doubling Time at Different Returns
| Yearly Return | Exact | Rule of 72 | Rule of 70 | Rule of 69.3 |
|---|---|---|---|---|
| 1% | 69.7 years | 72.0 years | 70.0 years | 69.3 years |
| 2% | 35.0 years | 36.0 years | 35.0 years | 34.6 years |
| 3% | 23.4 years | 24.0 years | 23.3 years | 23.1 years |
| 4% | 17.7 years | 18.0 years | 17.5 years | 17.3 years |
| 5% | 14.2 years | 14.4 years | 14.0 years | 13.9 years |
| 6% | 11.9 years | 12.0 years | 11.7 years | 11.5 years |
| 7% | 10.2 years | 10.3 years | 10.0 years | 9.90 years |
| 8% | 9.01 years | 9.00 years | 8.75 years | 8.66 years |
| 9% | 8.04 years | 8.00 years | 7.78 years | 7.70 years |
| 10% | 7.27 years | 7.20 years | 7.00 years | 6.93 years |
| 12% | 6.12 years | 6.00 years | 5.83 years | 5.77 years |
| 15% | 4.96 years | 4.80 years | 4.67 years | 4.62 years |
| 20% | 3.80 years | 3.60 years | 3.50 years | 3.46 years |
| 25% | 3.11 years | 2.88 years | 2.80 years | 2.77 years |
The rule of 72 is most accurate around 8%; the rule of 70 does better at low rates such as inflation.
What the Rule of 72 Says
Divide 72 by a yearly growth rate to estimate how many years it takes to double: at 8%, 72 ÷ 8 = 9 years (the exact answer is 9.01). It works the other way too: to double in 6 years you need about 12% a year. The same idea shows how fast inflation halves your money's buying power, or how quickly a debt doubles.
The Formulas
Years to double ≈ 72 ÷ rate
Rate needed ≈ 72 ÷ years
Exact: years = ln 2 ÷ ln(1 + rate)
Rates are in percent, e.g. 8 for 8%.
Using the Rule
- •At 3% inflation, prices double in about 24 years
- •A credit card at 24% doubles an unpaid balance in about 3 years
- •Fees matter: cutting 1 point of fees can add years of extra growth
- •Use 70 instead of 72 for low rates like inflation
- •The rule assumes returns compound and stay steady