Rule of 72 Calculator
A quick way to estimate how long it takes to double your money.
What Is the Rule of 72?
The Rule of 72 is a mental shortcut for estimating how long it takes an investment to double at a fixed annual return: just divide 72 by the interest rate. It's not exact, but it's close enough for quick decisions and easy to do in your head.
Years to Double ≈ 72 / Interest Rate
Worked Example
At 8% annual return, the Rule of 72 estimates 72 ÷ 8 = 9 years to double your money. The exact mathematical answer (using logarithms) is 9.01 years — remarkably close.
Disclaimer
This is a mathematical estimate, not a guarantee of investment performance. Not financial advice.