Rule of 72 Calculator
Estimate years to double or required rate using the Rule of 72 alongside more precise calculations.
Key Results
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
How we calculate
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.
Quick Answer
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)).
Key Facts
- Rule of 72 is a quick mental estimate for doubling time
- Rule of 69.3 suits continuous compounding; 70 is a common variant
- Exact time depends on compounding frequency
- Higher rates shorten doubling time; lower rates lengthen it
Adjust Interest Rate
See how interest rate changes affect doubling time
Personalized Insights
2 insights based on your inputs
Good News
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.
Note
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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Frequently Asked Questions
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.