Tool 10 of 10

Rule of 72 Doubling-Time Estimator

ReviewedLast reviewed Oct 2026 · Educational formulas

Estimate how long it takes money to double at a given rate, or the rate needed.

Inputs

Enter a rate (%) or a number of years, depending on the option above.

Results

Enter your values and press Calculate. Results update live after the first calculation.

How it works

The Rule of 72 is a mental shortcut: Years to double ≈ 72 ÷ rate %. It is most accurate for rates around 6–10%. The Rule of 70 and 69.3 are close alternatives.

We also show the exact answer for annual compounding: ln(2) ÷ ln(1 + r), so you can see how close the shortcut is.

Estimates for educational purposes only. Results are approximations and not financial advice. See the disclaimer.