Tools · Rule of 72
How fast does your money double?
The Rule of 72 is the back-of-napkin trick every investor knows: divide 72 by your return to get the years to double. Run it either way below.
Your money doubles in
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Doubling time at a glance
An approximation, most accurate for ~6–10% returns. Education, not financial advice.
Frequently asked questions
What is the Rule of 72?
A shortcut for how long an investment takes to double: divide 72 by the annual return %. At 8% a year, money doubles in ~72 ÷ 8 = 9 years.
How accurate is the Rule of 72?
A close approximation for rates between about 6% and 10%. At very low or very high rates it drifts slightly from the exact figure, but it's accurate enough for quick mental math and planning.
How long to double my money at 7%?
About 10.3 years (72 ÷ 7). At 10% it's ~7.2 years, and at 4% about 18 years — higher returns shorten doubling time dramatically.
When should I use the Rule of 72?
For a fast gut-check on compounding, or to work backward to the return you'd need to double money by a date. For precise projections, use the compound interest calculator.