Rule of 72 Calculator
Enter an annual rate of return to estimate how many years it takes for your money to double. At 8% the Rule of 72 gives 9 years.
How the Rule of 72 works
The Rule of 72 is a quick mental shortcut. Divide 72 by the annual rate of return, as a whole number, and the result is the approximate number of years it takes an investment to double with compound growth. At 8 percent, 72 divided by 8 is 9 years.
The calculator above also shows the exact figure, which uses the compound interest formula, so you can see how close the shortcut gets. The rule is most accurate for rates between about 6 and 10 percent. At very low or very high rates it drifts a little.
The formulas
Example: At 8 percent the rule says 9 years. The exact answer is 9.01 years, a difference of 0.01 years. Starting with $10,000, the balance at the doubling point is $20,000.00.
Using it the other way
You can also work backwards. To double your money in 6 years you need about 72 divided by 6, or 12 percent a year. The rule only applies to compound growth with no withdrawals and a steady rate, and it ignores fees and taxes. Returns are never guaranteed, so treat the answer as an estimate. For full growth projections see our compound interest calculator.
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Frequently asked questions
What is the Rule of 72?
It is a shortcut: divide 72 by the annual rate of return to estimate the years needed to double an investment.
How accurate is the Rule of 72?
It is closest for rates of about 6 to 10 percent. For 8 percent it gives 9 years against an exact 9.01 years.
Can I use it for inflation or debt?
Yes. At 3 percent inflation prices double in about 24 years, and a debt growing at 18 percent doubles in about 4 years.
Does it work for tripling money?
The rule is for doubling. Use a different constant, about 114 for tripling, or the exact formula.
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