Rule of 72 Calculator
Estimate how long it takes to double your money at a given return — or the return needed to double in a set time — with the exact answer for comparison.
For information and education only — not financial advice. Results are estimates based on the numbers you enter; check important decisions with a qualified professional.
How to use
- 1Enter an annual return to see the doubling time.
- 2Or switch mode and enter the years to find the return needed.
How it's calculated
Years to double ≈ 72 ÷ rate. Exact: ln 2 ÷ ln(1 + rate). The rule is most accurate for rates between 6% and 10%.
Frequently asked questions
Why 72?
It's close to 100 × ln 2 (69.3) adjusted for typical rates, and it divides evenly by many numbers (2, 3, 4, 6, 8, 9, 12).
Does it work for debt?
Yes — a card balance at 24% APR roughly doubles in 3 years if nothing is paid.
What about inflation?
At 3% inflation, prices double in about 24 years — so money loses half its value in that time.