Rule of 72 Calculator
Estimate investment doubling time or the annual return needed to double your money. The calculator also compares the Rule of 72 estimate with the exact compounding result.
Choose whether you want to estimate doubling time or the required annual rate.
Required when finding how long it takes to double.
Required when finding the annual rate needed.
Estimated annual rate = 72 / years to double
Exact doubling time = ln(2) / ln(1 + r)
What is the Rule of 72?
The Rule of 72 is a quick estimate that tells you how long it takes for money to double at a given annual return. Divide 72 by the annual rate to estimate years, or divide 72 by years to estimate the rate needed.
How accurate is the Rule of 72?
It is an approximation, not an exact formula. It is usually most accurate for returns in the mid-single-digit to low-double-digit range. This calculator also shows the exact doubling figure so you can compare the shortcut to the mathematically precise result.
Why use 72 instead of 70 or 69.3?
The exact natural-log based doubling constant is closer to 69.3, but 72 is easy to divide by many common rates such as 6, 8, 9, and 12. That convenience is why the Rule of 72 is widely used in personal finance and investing education.
Can I use the Rule of 72 for debt too?
Yes. The same shortcut can help estimate how quickly debt grows when interest compounds and payments are not keeping up. It is often used to show how expensive high-interest debt can become over time.
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📐 Formula
Estimated annual rate = 72 / years to double
Exact doubling time = ln(2) / ln(1 + r)