Rule of 72 calculator

Divide 72 by an annual return in percent to estimate how long a balance takes to double. The page also shows the exact compound-interest doubling time at that same rate. The Rule of 72 guide uses the same example.

Years to double ≈ 72 ÷ annual return in percent. Exact years = natural log of 2 ÷ natural log of (1 + annual rate).

Rule of 72

Enter an annual return and a starting amount.

How to estimate a doubling time

Enter an annual return. Use percent, so 8 means 8% a year. The rate stays constant for every doubling.
Compare the shortcut with the exact years. The Rule of 72 divides 72 by the percent. The exact line uses compound interest.
Read the milestone balances. Each milestone applies the exact doubling time to the starting amount. The balance doubles, then doubles again.

Frequently asked questions

How does the Rule of 72 work?: Divide 72 by the annual return in percent. At 8%, 72 ÷ 8 is 9 years. The exact compound-interest doubling time at 8% is also about 9.01 years. The shortcut is closest for rates near 8%.
What is the exact doubling time?: Exact years equal the natural log of 2 divided by the natural log of 1 plus the annual rate. The calculator shows that figure next to the Rule of 72 so you can see the gap at the rate you typed.
Is this investment advice?: No. The calculator is for general informational and educational purposes only. A doubling time describes a constant rate. It does not predict the return of any security.

Related guides

How to estimate a doubling time

Enter an annual return. Use percent, so 8 means 8% a year. The rate stays constant for every doubling.

Compare the shortcut with the exact years. The Rule of 72 divides 72 by the percent. The exact line uses compound interest.

Read the milestone balances. Each milestone applies the exact doubling time to the starting amount. The balance doubles, then doubles again.

Frequently asked questions

How does the Rule of 72 work?

Divide 72 by the annual return in percent. At 8%, 72 ÷ 8 is 9 years. The exact compound-interest doubling time at 8% is also about 9.01 years. The shortcut is closest for rates near 8%.

What is the exact doubling time?

Exact years equal the natural log of 2 divided by the natural log of 1 plus the annual rate. The calculator shows that figure next to the Rule of 72 so you can see the gap at the rate you typed.

Is this investment advice?

No. The calculator is for general informational and educational purposes only. A doubling time describes a constant rate. It does not predict the return of any security.

Rule of 72

How to estimate a doubling time

Frequently asked questions

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Rule of 72

How to estimate a doubling time

Frequently asked questions

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