Rule of 72 Calculator
Estimate how long it takes to double your money.
Input
Years to Double
Investment doubles by 2036
Divide 72 by your annual return rate to estimate the years needed to double your investment. It works in reverse too: divide 72 by your target years to find the required annual rate.
Doubling Timeline
@ 7% annual return
Asset Comparison
Inflation Impact
The Rule of 72 also reveals how fast inflation erodes purchasing power. At 3% annual inflation, prices double in just 24 years — meaning your money's purchasing power is cut in half.
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Using the Rule of 72 to Estimate Doubling Time
Overview
The Rule of 72 is a quick mental shortcut for how long it takes an investment to double at a fixed annual return: just divide 72 by the rate. It is remarkably accurate for typical rates and great for sanity-checking growth without a spreadsheet. This calculator applies it instantly, and also works in reverse to find the rate needed to double in a given time.
How to Use (Step by Step)
- 1
Enter the annual rate
The expected yearly return or interest rate as a percentage.
- 2
Read the doubling time
The tool divides 72 by the rate to estimate years to double.
- 3
Or solve for the rate
Enter a target number of years to see what annual rate doubles your money in that time.
How It Works
Years to double ≈ 72 ÷ annual interest rate (as a percent). At 8%, money doubles in about 9 years; at 6%, about 12 years. The 72 works because it closely approximates the exact logarithmic doubling formula for rates between roughly 4% and 15%. To find the required rate instead, divide 72 by the number of years you have.
When to Use This
Quickly estimating how fast savings will grow. Comparing the long-term impact of different return rates. Showing how inflation erodes purchasing power (how fast prices double).
Frequently Asked Questions
Very close for rates between about 4% and 15%. At higher or lower rates the approximation drifts slightly from the exact figure, but it remains a useful estimate.
Important Notes
The Rule of 72 is a rough mental-math approximation, not investment advice. Real returns are not fixed and are not guaranteed — consult a licensed financial advisor before making investment decisions.