Estimate years to double or required rate using the Rule of 72 alongside more precise calculations.
Rule of 72
9.00 yrs
Quick estimate
Rule of 70
8.75 yrs
Alternate constant
Rule of 69.3
8.66 yrs
Continuous compounding
Exact
9.01 yrs
ln(2) based
Rule-of-thumb estimates divide 72 (or 70/69.3) by the rate. Exact time uses ln(2) / (n × ln(1 + r/n)) for the chosen compounding frequency.
Rule of 72: Years to double ≈ 72 ÷ rate. For example, at 8% it takes about 9 years. Exact doubling time is ln(2) / (n × ln(1 + r/n)).
See how interest rate changes affect doubling time
2 insights based on your inputs
At 8%, the Rule of 72 is highly accurate—only 0.1% off from the exact calculation. This is the sweet spot for this quick estimation method.
Your investment doubles in 9.0 years at 8%. After another 9.0 years, it quadruples. In 27 years, it's 8x your original investment.
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It is a close approximation for moderate rates (6%-10%). For precision or very high/low rates, use the exact calculation with compounding.
Rule of 70 is another quick estimate; 69.3 aligns with continuous compounding. The calculator shows all three plus the exact result.
Yes. Enter your target doubling time and the tool will compute the required annual rate, alongside rule-of-thumb comparisons.