Rule of 72 Calculator

Estimate how long money takes to double, or what annual return is needed to double within a target period.

Calculation mode

Rule of 72 inputs

Estimate how long it takes money to double, or the return needed to double within a target period.

Annual return

Starting amount

Rule of 72 estimate

9 years

Actual annual compounding

9.01 years

Effective annual return

Doubled amount

$20,000

Multiple timeline

9.01 years

14.27 years

18.01 years

20.91 years

10x

29.92 years

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What is the Rule of 72?

The Rule of 72 estimates how long compound interest takes to double money. Divide 72 by the annual return percentage to get the approximate doubling period.

Rule of 72 formula

Doubling years = 72 / annual return (%)

At 6% per year, 72 / 6 = 12 years.

Why 72 works

Mathematical background

From the compound-interest equation, doubling means 2 = (1 + r)^t.
Solving gives t = ln(2) / ln(1 + r), approximately 0.693 / r.
When r is expressed as a percent, the mathematically pure shortcut is about 69.3 / return.
72 is widely used because it divides cleanly by 2, 3, 4, 6, 8, 9, and 12 and is most accurate around 6% to 10% returns.

Other multiples

2x uses 72, so at 6% it takes about 12 years.
3x uses 114, so at 6% it takes about 19 years.
4x uses 144, so at 6% it takes about 24 years.
5x uses 168, so at 6% it takes about 28 years.
10x uses 240, so at 6% it takes about 40 years.

Examples and cautions

Planning examples

At 3% deposit interest, money doubles in about 24 years. The Korean guide identifies this as the 2026 fixed-deposit reference level.
At 8% equity-fund return, money doubles in about 9 years, shortening the 3% deposit path by 15 years.
A 35-year-old who wants 4x assets by age 60 has 25 years. Two doublings require about 12.5 years each, so the needed return is 72 / 12.5 = about 5.8%.
At a nominal 7% return and 2% inflation, real return is about 5%, so nominal doubling takes 10.3 years but purchasing-power doubling takes 14.4 years.

Limits and tax notes

The Rule of 72 assumes a constant annual compound return, so volatile investments can differ substantially from the shortcut.
Interest income tax of 15.4% and capital gains tax can lengthen the actual doubling period.
For negative returns, the same shortcut estimates halving time. A -6% annual loss halves capital in about 12 years.
For monthly contribution plans, use a compound-interest or IRR calculator because the Rule of 72 works best for lump-sum investing.