Rule of 72
A shortcut to estimate how many years it takes an investment to double: divide 72 by the annual return.
The Rule of 72 is a quick mental estimate for doubling time. Divide 72 by your annual rate of return and you get the approximate number of years for money to double. At 8% a year, money doubles in about 9 years (72 / 8); at 6%, about 12 years.
It's a back-of-envelope tool, not a precise formula, but it's remarkably useful for building intuition about compounding — and about inflation working in reverse (at 3% inflation, prices double in about 24 years, halving your purchasing power). It's a fast way to sanity-check whether a growth assumption is reasonable.
This definition is general information to help you understand a term, not financial, tax, or legal advice. Figures that change year to year (limits, thresholds, rates) should be confirmed against current official sources. For guidance on your situation, a licensed fee-only fiduciary is the right next step.