Rule of 72 Calculator
The Rule of 72 is the fastest mental math in finance: divide 72 by your return to get the years to double. See it in action.
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Learn moreMental math for compounding
The Rule of 72 turns compounding into a quick estimate: 72 ÷ your return = years to double. It’s remarkably accurate for typical rates and makes the power of compounding (and the cost of inflation) intuitive without a spreadsheet. Sister rules — 114 and 144 — estimate tripling and quadrupling.
How it’s calculated & sources
Years to double ≈ 72 ÷ rate. Tripling uses 114 ÷ rate; quadrupling uses 144 ÷ rate. These approximations are closest for rates in the mid single digits to low teens.
Benchmark: the Rule of 72 — a classic, accurate-enough shortcut for the doubling time of compound growth.
Results update as you type and are general estimates, not personalized financial, tax, medical or legal advice. Verify with a professional.
Worked example
At an 8% return, money doubles in about 9 years, triples in ~14 years, and quadruples in ~18 years. So $10,000 becomes $20,000 in roughly 9 years.
Frequently asked questions
How accurate is it?
Very, for rates around 6–10%. At higher rates it slightly overstates the time; 69.3 is the mathematically exact constant, but 72 divides more cleanly.
Does it work for inflation?
Yes — divide 72 by the inflation rate to see how fast prices double (and your money’s buying power halves).