Rule of 72 Calculator
The Rule of 72 is a handy shortcut for doubling time that you can almost do in your head. Slide the annual return and see how many years it takes to double, plus how 1,000 dollars would grow over 40 years.
At 8%, your money doubles about every 9.0 years (72 ÷ 8). $1,000 becomes $21,725 in 40 years.
Worked examples
Real results from this calculator, computed for a few common scenarios. Move the sliders above to run your own numbers.
| Annual return = 5% | At 5%, your money doubles about every 14.4 years (72 ÷ 5). $1,000 becomes $7,040 in 40 years. |
| Annual return = 10.5% | At 10.5%, your money doubles about every 6.9 years (72 ÷ 10.5). $1,000 becomes $54,261 in 40 years. |
| Annual return = 16% | At 16%, your money doubles about every 4.5 years (72 ÷ 16). $1,000 becomes $378,721 in 40 years. |
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How this math works
Divide 72 by your annual return percent and you get the approximate number of years for your money to double. At 8 percent, that is about 9 years.
The calculator also charts 1,000 dollars compounding at your chosen rate across 40 years, so you can see how repeated doublings add up over a working lifetime.
Common questions
How accurate is the Rule of 72?
It is a close approximation, most accurate for returns between about 6 and 10 percent. For rates far outside that range the estimate drifts slightly from the exact doubling time.
Why 72 and not another number?
72 is used because it divides evenly by many common returns and lands very near the precise mathematical answer. It is chosen for easy mental math.
Does this include inflation?
No. The doubling is in nominal terms. If you want doubling in buying power, use a return figure that already has inflation subtracted.
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