Formula
Years to double ≈ 72 ÷ annual rate (%). Exact: ln(2) ÷ ln(1 + rate).
About this calculator
The rule of 72 is a mental shortcut. It is most accurate for rates between about 6% and 10%; the exact logarithmic result is shown beside it.
Amounts are shown without a currency symbol, so the calculator works for any currency: enter all values in the same one.