This free Rule of 72 calculator estimates exactly how many years it takes for your investment to double at a given annual return rate. The Rule of 72 calculator is a quick mental-math shortcut investors have used for decades — just divide 72 by your annual return rate to estimate doubling time, no compound interest formula required.
Years to Double Your Money
9.0
at 8% annual return
Doubling Timeline — Starting at $1,000
$1,000
Year 0
$2,000
Year 9
$4,000
Year 18
$8,000
Year 27
$16,000
Year 36
$32,000
Year 45
Common Return Rates
4% annual return18.0 years to double
6% annual return12.0 years to double
8% annual return9.0 years to double
10% annual return7.2 years to double
12% annual return6.0 years to double
At the S&P 500's historical ~10% average annual return, your money doubles approximately every 7.2 years.
How to use this calculator
Enter your expected annual return rate
See instantly how many years until your investment doubles
Compare against common return rates (4%, 6%, 8%, 10%, 12%)
Visualize the doubling timeline starting from $1,000
What is the Rule of 72?
The Rule of 72 is a simplified way to estimate how long an investment takes to double in value, given a fixed annual rate of return. Divide 72 by your annual return percentage, and the result is approximately the number of years to double your money. It's not perfectly precise — the real formula uses natural logarithms — but the Rule of 72 is accurate within a few months for return rates between 6% and 10%, making it a fast mental-math tool investors have relied on for generations.