Rule of 72 Calculator (Investment Doubling Time)
S&P 500 historical average: ~10-11% annually
About the Rule of 72
Rule of 72: Years to double = 72 / Annual return rate (%)
Reverse: Required rate = 72 / Target years
Exact formula: Years = ln(2) / ln(1 + r)
Example: At 8% return, investment doubles in 72/8 = 9 years
Why 72? It has many divisors, making mental math easier, and it\'s accurate for typical investment returns (6-10%).
About This Calculator
Rule of 72 Calculator (Investment Doubling Time) is designed to reduce manual errors and give repeatable outputs when you need quick, reliable answers.
Estimate how long an investment takes to double using a quick mental-math approximation for return-rate planning.
If your workflow expands, pair this calculator with Compound Interest Calculator and Present Value / Future Value Calculator to cross-check assumptions and build a stronger analysis chain.
Formula
Doubling Time (years) ~= 72 / annual return rate (%)
Example Calculation
The worked example below demonstrates how the input fields translate into the final output. Use it as a quick validation pass before entering your own numbers.
- annualReturnPercent: 8
Explanation of Results
Result Interpretation
At 8% return, the rule estimates doubling near 9 years, useful for fast scenario benchmarking.
FAQ
How accurate is Rule of 72?
It is a close approximation for moderate return rates, but exact compound calculations are better for final planning.
Can it be used for debt growth?
Yes. The same logic can estimate how quickly debt may double at a given interest rate.
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See Also
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