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How to use Rule of 72 Calculator

Enter an annual interest or growth rate. The calculator shows the Rule of 72 doubling-time estimate next to the exact compounding answer for comparison.

Frequently asked questions

What is the Rule of 72?

It is a shortcut: divide 72 by the annual interest rate to estimate the years needed to double your money. At 8%, that is 72 ÷ 8 = about 9 years.

How accurate is the Rule of 72?

It is a close approximation for rates between roughly 6% and 10%. For very high or low rates the exact logarithmic formula, also shown here, is more precise.

What is the exact doubling formula?

The precise time to double is ln(2) / ln(1 + r), where r is the annual rate. This calculator shows both the Rule of 72 estimate and this exact value.

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