Rule of 72 Calculator
Estimate how long it takes an investment to double, triple, or quadruple at a given annual return using the Rule of 72, 114, and 144.
Doubling time shortcut
Years to double (Rule of 72)
10.29 years
At 7.00% per year, your money would double in about this amount.
Exact value (logarithms)
10.24 years
Approximation error
0.40%
Frequently Asked Questions about the Rule of 72 Calculator
What is the Rule of 72 and how does it work?
The Rule of 72 is a mental-math shortcut for estimating how many years it takes an investment to double at a fixed annual return. Divide 72 by the rate in percent. At 8% per year, money roughly doubles every 72 / 8 = 9 years. The exact answer uses logarithms, but 72 gives you a fast, close estimate.
How accurate is the Rule of 72?
It is most accurate for rates between 6% and 10%, where the error stays under about 1%. At lower rates the Rule of 70 fits better, and at higher rates the approximation drifts. This calculator shows the exact logarithmic answer next to the rule estimate so you can see the gap.
What is the difference between the Rules of 72, 114, and 144?
Same shortcut, different growth targets. Use 72 for doubling, 114 for tripling, and 144 for quadrupling. So a 6% return triples money in roughly 114 / 6 = 19 years and quadruples it in about 144 / 6 = 24 years.
Can I use the Rule of 72 to find the rate I need?
Yes. Flip the formula: 72 divided by the years you have gives the approximate annual return required to double. To double in 10 years you need about 7.2% per year; the exact figure is closer to 7.18%.
Does the Rule of 72 account for inflation, taxes, or fees?
No. It uses a clean annual rate, so subtract inflation, taxes, and investment fees from your assumed return before plugging it in. If you expect 8% nominal returns and 3% inflation, use 5% to estimate real doubling time, which gives about 14.4 years.