Rule of 72 Calculator
Estimate how long money takes to double at a rate, or the rate needed to double in a time, with the exact answer.
Change the values and press Calculate to work out your own figures.
Years to double
Enter the rate.
Show the working
- years ≈ 72 ÷ rate
- exact = ln 2 ÷ ln(1 + rate)
Rate to double
Enter the years.
Show the working
- rate ≈ 72 ÷ years
- exact = 2^(1/years) − 1
How to use it
Enter the rate. Enter the years.
Enter amounts without commas or with them; rates are percentages (5 for 5%). Negative amounts are allowed where a sign means money paid out.
Key facts
years ≈ 72 ÷ rate; exact years = ln 2 ÷ ln(1 + rate)
Accuracy
The rule of 72 is closest around 8%; at 1% the exact answer is 69.66 years, at 20% it's 3.8.
Questions
How long to double at 3%?
About 24 years (exactly 23.45).
Formulas
years ≈ 72 ÷ rate; exact years = ln 2 ÷ ln(1 + rate)
Sources
Limitations
- Results are estimates for planning, not offers or financial advice; lenders and banks may round, count days or time payments differently.
- Rates are nominal annual rates compounded as you choose; payments at a different frequency use the equivalent periodic rate.