Quickly estimate how long it takes to double your money
A mental shortcut for how long money takes to double: divide 72 by the annual growth rate. It works because ln(2) is about 0.693, and 72 divides cleanly by 2, 3, 4, 6, 8, 9, and 12.
Years to double ≈ 72 / rate (as a whole-number percent)
rateannual compound growth rate, entered as a percent (8 for 8%)Exact formln(2) / ln(1 + r), which the rule approximatesYes. Rule Of 72 costs nothing, needs no account, and runs right in your browser. There is no paywall, no watermark on the results, and no limit on how many times you can run the numbers.
Rule Of 72 uses the standard formula for this kind of calculation, so the output is only as good as the figures you type in. Rates, fees, and rules in finance shift over time, and we review the underlying assumptions on a regular schedule; check the "Last reviewed" date above for the most recent pass. Spotted something off? There's a feedback button in the bottom-right corner.
Treat the output of Rule Of 72 as a starting point, not final advice. Tax filings, loan approvals, insurance claims, property deals, and legal matters all depend on details a calculator cannot see: your full financial picture, local rules, and the specifics of your paperwork. Run the numbers here, then confirm anything consequential with an accountant, lawyer, or licensed advisor.