Rule of 72 Calculator
Doubling time from any return — the mental-math rule versus the exact logarithmic answer.
Formula
Disclaimer: Mental-math approximation for education; exact values computed alongside. Not financial advice.
Need rule of 72 calculator results fast? Skip the spreadsheet and get a clear, defensible answer in one step — free, private and instant, recalculating live as you change any input.
About Rule of 72 Calculator
The rule of 72 is the most useful piece of financial mental math ever devised: divide 72 by the annual return and you get the years to double — 12% doubles in ~6 years, 8% in ~9, 6% in ~12. This calculator shows the rule beside the exact logarithmic answer so you can see how good the approximation really is (remarkably: within 2% error for rates between 5% and 12%). The 'doublings in 30 years' output is where intuition gets built: at 12%, thirty years holds ~4.9 doublings — a 30× multiple; at 8%, ~2.9 doublings for 7.5×; at 4% (post-tax FD territory), ~1.7 doublings for 3.2×. Wealth differences between asset classes aren't percentages — they're COUNTS OF DOUBLINGS, which is why a few points of return compound into different lives over a career. Use 72's siblings for adjacent questions: rule of 114 for tripling time, 144 for quadrupling, and — the dark mirror — 72 ÷ inflation for how fast prices double (6% inflation doubles costs every 12 years, exactly the doubling your investments must out-race). The rule also inverts: to double in N years you need 72/N percent — doubling in 5 years demands ~14.4%, a useful smell test for any scheme promising it at 'no risk'.
How to use Rule of 72 Calculator
- 1Enter Annual return (%) into the Rule of 72 Calculator.
- 2The result is computed automatically using Years to double ≈ 72 ÷ rate ; exact = ln(2) ÷ ln(1 + rate) — there is no button to press; it updates live as you type.
- 3Change any input to model a different scenario, then use “Copy result link” to share the exact numbers.
Why use Rule of 72 Calculator?
- ✓Computes rule of 72 calculator instantly with the correct formula — no spreadsheet needed
- ✓100% free and unlimited, with no sign-up, login or paywall
- ✓Runs entirely in your browser, so the figures you enter are never uploaded or stored
- ✓Shows the formula, a live worked example and references so you can defend the number
Frequently asked questions
How accurate is the rule of 72?+
Excellent in the everyday range: between 5% and 12% the error stays under ~2% (the output above shows yours precisely). It drifts at extremes — for very low rates 69.3 is technically better; for 20%+ the rule underestimates slightly. For mental math on normal investments, 72 is the right constant.
Paisa kitni baar double hoga 25 saal me?+
Rate se ginti karein: 12% par har ~6 saal me ek double → 25 saal me ~4 doublings = 16×. 8% par ~2.8 doublings = 7×. 6.5% FD (pre-tax) par ~2.2 = 4.7× — aur tax ke baad usse kam. Doublings ki ginti hi long-term planning ka sabse imaandaar nazariya hai.
What return doubles money in 5 years?+
72 ÷ 5 ≈ 14.4% per year (exact: 14.87%). That's above long-run equity averages — achievable in good periods, not promisable. Any product GUARANTEEING a 5-year double is claiming to beat the world's best investors with no risk; the rule of 72 is your one-line fraud detector.
Does the rule work for inflation and fees too?+
Beautifully: 72 ÷ 6% inflation = prices double every 12 years (your retirement corpus must fund that). And a 1.5% expense-ratio difference compounds the same way — over 24 years high fees eat roughly one ENTIRE doubling of your wealth. Same math, three directions: returns, inflation, costs.
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