What is the Rule of 72?

The Rule of 72 is a quick formula used to estimate the number of years required to double your money at a given annual return rate.

Rule of 72 Calculator

Estimate how long it will take for your money to double at a given fixed interest rate.

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Parameters

R Reset

Interest Rate (%)Annual Percentage Rate (APR). US average 30yr mortgage: ~7%.

8.0%

0.1%100.0%

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Years to Double

9.00 Years

Interest Rate8%

Exact Doubling Time9.01 Years

Result Interpretation

Historical mid-range compounding velocity at an interest rate of 8.00%, requiring 9.00 years to double capital per Fidelity Savings and Compounding Guidelines.

Mathematical Explanation

t \approx \frac{72}{R}

At an annual interest rate of 8%, your money will double in approximately 9.00 years (72 ÷ 8). The exact compounding formula yields a doubling time of 9.01 years.

How to Use the Rule of 72 Calculator

The Rule of 72 is a simple, shorthand method to estimate how many years it will take for an investment to double in value, given a fixed annual rate of interest.

Input variables:

Interest Rate (%): Bounded parameter in the mathematical model.