About the Rule of 72
The Rule of 72 is a quick way to estimate how long an investment takes to double: divide 72 by the annual rate of return. This calculator works both ways — years to double from a rate, or the rate needed to double in a given time. It runs in your browser.
How Rule of 72 works
How to use it
- Pick whether you know the rate or the years.
- Enter the value.
- Read the estimate.
How it works
Years to double ≈ 72 ÷ rate, and rate to double ≈ 72 ÷ years. It is an approximation of the exact compound-interest doubling time, most accurate for rates around 6–10%.
Common uses
- Estimate years to double money
- Find the rate to double in X years
- Compare investment growth
- Teach compound interest
- Make quick mental estimates
- Plan savings goals
- Sanity-check returns
- Learn the Rule of 72
Frequently asked questions
What is the Rule of 72?
A shortcut: 72 ÷ rate estimates the years for money to double.
How accurate is it?
Very close for rates around 6–10%; less so at extremes.
Can I find the rate instead?
Yes — divide 72 by the years to get the rate needed.
Is my input uploaded?
No — it calculates in your browser.
Why 72?
72 has many divisors and closely matches the exact maths for typical rates.
Does it use compounding?
It approximates annual compounding.
Is it free?
Yes — completely free with no sign-up.