Rule of 72 Calculator
Estimate how long it takes to double your money at any interest rate using the Rule of 72.
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Rule of 72: Divide 72 by your annual rate to estimate years to double. At 6%, your money doubles every 12.0 years.
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Years to Double
0Doublings in 50 Years
0Balance After 50 Years
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See your money double over 50 years
Results are for informational purposes only and do not constitute financial advice. Actual returns may vary due to market conditions, taxes, and fees. Read our full disclaimer.
What is the Rule of 72?
The Rule of 72 is one of the most useful mental math shortcuts in personal finance. Divide 72 by your annual interest rate and you get the approximate number of years it takes to double your money. At 6%, your money doubles in 12 years. At 9%, it doubles in 8 years. At 12%, just 6 years. The rule works because 72 is mathematically close to the natural logarithm calculation that governs exponential growth.
How Accurate is the Rule of 72?
The rule is remarkably accurate for interest rates between 6% and 10%. At exactly 8%, the rule predicts 9 years — the precise mathematical answer is 9.006 years. At lower or higher rates the approximation drifts slightly: at 2% the rule says 36 years while the true answer is 35. At 20% the rule says 3.6 years while the true answer is 3.8. For practical financial planning, this level of precision is more than sufficient.
The Rule of 72 in Reverse
You can also run the rule backwards: divide 72 by the number of years to find the rate required to double your money. Want to double in 10 years? You need a 7.2% annual return. Want to double in 6 years? You need 12%. This reverse application is especially useful when evaluating whether an investment's promised return is realistic given your time horizon. The rule also applies to inflation — at 3% inflation, prices double in 24 years, meaning your cash loses half its purchasing power in just over two decades.