Quickly estimate how long it takes for an investment to double at a given interest rate.
Enter values and click Calculate to see results
Years to double ≈ 72 / annual rate. The exact figure is ln(2) / ln(1 + rate); the Rule of 72 approximates it well between roughly 4% and 10%.
Very accurate for typical rates: at 6% it gives 12.0 years versus the exact 11.9; at 8%, 9.0 versus 9.01. It drifts at extreme rates (above ~12% or below ~3%).
Yes — in reverse. To find the rate needed to double in N years, divide 72 by N. Doubling in 10 years requires about a 7.2% return.