Rule of 72 calculator
Use the rule of 72 shortcut to see how fast money doubles, and compare it with the exact answer. It is a quick check for savers, investors and finance students.
- Runs in your browser
- Free, no account needed
- Copy or download the result
Result
Example
Solve for: Years to double Annual rate: 8 Years to double: 10
Rule of 72 estimate: 9 years Exact years to double: 9.01 years Difference: 0.01 years Rule of 72: years = 72 / rate. Exact: years = ln(2) / ln(1 + rate), with growth compounded once a year. The shortcut is most accurate for rates near 8%.
How to use the rule of 72 calculator
- Under Solve for, choose Years to double or Rate needed to double.
- Enter the Annual rate, or the Years to double for the rate mode.
- Press Run to see the estimate and the exact value.
- Press Copy result to keep it.
How it works
Rule of 72 estimate: years = 72 / rate, or rate = 72 / years.
Exact answers use yearly compounding: years = ln(2) / ln(1 + rate), and rate = 2^(1 / years) - 1.
The shortcut is most accurate for rates near 8% and drifts further off at high rates.
The rate must be greater than 0% and up to 100%, and years greater than 0 and up to 100.
Everything runs in your browser. Your input is not uploaded or stored.
Questions and answers
What is the rule of 72?
It is a shortcut: divide 72 by the yearly rate to estimate how many years it takes money to double. At 8%, that is about 9 years.
How accurate is the rule of 72?
It is close for typical rates. At 8% the estimate is 9 years and the exact answer is about 9.01 years.
What rate doubles money in 10 years?
The rule of 72 says 7.2%. The exact rate with yearly compounding is about 7.18%.