CALCULATOR
Rule of 72 Calculator
Divide 72 by your rate of return and you get roughly the years it takes to double your money. It is a good shortcut and a poor precision tool, so both numbers are shown.
The curve, and where it doubles
Doubling again and again
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The Rule of 72 is a mental shortcut: divide 72 by the rate to approximate the years to double. It drifts from the precise figure at high rates, which is why both are shown. It assumes a steady return and ignores fees and tax.
These numbers are a starting point. Talk to an advisor about your own situation.
Talk to an AdvisorHow long does it take to double your money?
Divide 72 by your annual rate of return and you get the approximate number of years for money to double. At 6% that is 12 years; at 9%, eight years. The shortcut is accurate to within a few months for rates between about 4% and 12%, and drifts further from the exact figure outside that range.
Common questions
Why 72 and not another number?
72 divides cleanly by many small whole numbers, which makes the arithmetic easy in your head. The mathematically exact constant is closer to 69.3, but 72 is more convenient and happens to be more accurate at the mid single-digit rates people usually use.
How accurate is the Rule of 72?
Very close between roughly 4% and 12%. At 6% it gives 12 years against an exact 11.9. At 20% the gap widens to several months, which is why the precise figure is shown alongside it above.
Does it work for inflation too?
Yes. Dividing 72 by an inflation rate tells you roughly how long until prices double, and therefore how long until your purchasing power halves.
Figures and sources
This calculator uses 2026 figures. Government amounts are reset regularly — CPP each January, OAS every quarter, tax brackets each January.
Last reviewed: 19 August 2026
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