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Rule of 72 Calculator

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Parameters
Annual Percentage Rate (APR). US average 30yr mortgage: ~7%.
8.0%
0.1%100.0%
%
Analytics Dashboard
Years to Double
9.00 Years
Interest Rate8%
Exact Doubling Time9.01 Years
Result Interpretation

Historical mid-range compounding velocity at an interest rate of 8.00%, requiring 9.00 years to double capital per Fidelity Savings and Compounding Guidelines.

Mathematical Explanation
t≈72Rt \approx \frac{72}{R}

At a fixed 8% effective annual rate, the Rule of 72 estimate is 9.00 years (72 ÷ 8). Under annual compounding with no cash flows, the logarithmic comparison is 9.01 years. Neither value predicts or guarantees an actual return.

How to Use the Rule of 72 Calculator

The Rule of 72 is a simple, shorthand method to estimate how many years it will take for an investment to double in value, given a fixed annual rate of interest.

Input variables:
  • Interest Rate (%): The annual compounding interest rate.

Rule of 72: How to Calculate Doubling Time with Interest

Learn the simple rule-of-thumb formula to quickly estimate capital doubling timelines based on interest rates.

Read Full Guide →