How long to double your money? Divide 72 by your expected rate of return. This mental math shortcut works for investments, inflation, debt, and population growth.
Rule of 72 Calculator
Time to double — or find the rate needed
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After Doubling
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Rule of 72 Estimate
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Exact (ln2/r)
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In 30 years
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Doublings in 30yr
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Doubling Time (72÷r)
$10K becomes
FAQ
What is the Rule of 72?
Divide 72 by an annual rate of return to estimate the number of years to double your money. At 6%, money doubles every 12 years (72÷6). At 12%, it doubles every 6 years. This is a mental shortcut — the exact formula uses the natural logarithm: years = ln(2)/ln(1+r).
Why 72 and not 70 or 69?
72 is a highly composite number (divisible by 1,2,3,4,6,8,9,12) making mental math easy. Rule of 70 is more accurate for lower rates; Rule of 72 is slightly better for higher rates (8-20%). For maximum accuracy use ln(2)/r.
Does the Rule of 72 work for inflation?
Yes! At 3% inflation, prices double in ~24 years (72÷3). At 7%, everything costs twice as much in just over 10 years. This is why investing to beat inflation is critical for long-term financial health.
Does it work for debt?
Yes — and it's alarming. Credit card debt at 24% APR doubles in 3 years if you make no payments (72÷24=3). This illustrates why high-interest debt is financially devastating and should be paid off immediately.