The Rule of 72 Calculator

Instantly calculate exactly how many years it will take for your investment to double in size.

Expected Annual Return %
Initial Investment (Optional) $
⚠️ Please enter an annual return rate greater than 0.
Time to Double (Rule of 72 Estimate)
10.3
Years
10.24 Exact Mathematical
Time Required (Years)
$20,000 Doubled Future
Value

What is the Rule of 72?

The Rule of 72 is a simplified formula that estimates how long it will take for an investment to double in value, based on a fixed annual rate of interest.

  • The Formula: Simply divide the number 72 by your expected annual interest rate. For example, if you expect an 8% return, it will take roughly 9 years to double your money (72 ÷ 8 = 9).
  • Why use the number 72? While 69.3 is technically the most mathematically accurate number for continuous compounding, the number 72 is used because it has so many easy divisors (1, 2, 3, 4, 6, 8, 9, 12). This makes it incredibly easy to do the math in your head without a calculator.
  • Is it accurate? As you can see in the calculator above, the Rule of 72 provides a surprisingly accurate estimate for interest rates between 4% and 15%. For extremely high or low interest rates, the exact mathematical formula becomes necessary.