How accurate is the Rule of 72?

It is very accurate for rates of 6–10%. For very low (1–2%) or very high (20%+) rates, the exact formula 'log(2)/log(1+r)' gives a more precise answer.

Can the Rule of 72 be used for inflation?

Yes. At 3% inflation, the purchasing power of money halves in 72 ÷ 3 = 24 years. This illustrates why inflation erodes savings over time.

Does the Rule of 72 work for debt?

Yes. At 18% APR credit card debt, the balance doubles in 72 ÷ 18 = 4 years if you make no payments. This shows the urgency of paying off high-interest debt quickly.

Rule of 72 Calculator

The Rule of 72 is a simple mental maths shortcut to estimate how long it will take for an investment to double in value at a fixed annual rate of return. Divide 72 by the annual interest rate and you get the approximate number of years to double your money. It also works in reverse — divide 72 by the number of years to find the required rate.

Annual Interest / Return Rate(%)

Frequently Asked Questions

The Rule of 72 is a quick estimate: Years to double = 72 ÷ Annual Rate. At 6% per year, your money doubles in 72 ÷ 6 = 12 years. It is accurate within 1–2% for rates between 6–10%.

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