Reckonary / Finance / Rule of 72 calculator
Years to double
The Rule of 72 is a shortcut for working out how long money takes to double at a steady rate of return. Divide 72 by the annual rate and you get the rough number of years. At 8% a year, that is 72 / 8, or about 9 years; at 6% it is 12. Drag the slider to see how a higher return shrinks the wait.
Doubling really follows compound growth, which uses logarithms. The exact answer comes from the natural log of 2 — about 0.693 — divided by the rate. Multiply that by 100 and you land near 69, but 72 is easier to divide in your head because it splits cleanly by 2, 3, 4, 6, 8, 9, and 12. For everyday rates between 5% and 12%, swapping 72 for the precise number barely changes the result.
Use it for any return that compounds: a savings account, a stock fund, or a retirement balance. It also runs in reverse for things that grow against you. At 6% inflation, prices double in roughly 12 years, so the same idea tells you how fast spending power can fade.
The Rule of 72 assumes one fixed rate and no deposits, withdrawals, taxes, or fees along the way. Real returns wobble year to year, so treat the answer as a quick gut check rather than a promise. For a decision that matters, run the exact compound numbers too.
Can I use the Rule of 72 to find the rate I need?
Yes. Run it backward: divide 72 by the number of years you have. To double your money in 8 years, you need about 72 / 8, or roughly a 9% annual return.
Is there a similar rule for tripling money?
Use the Rule of 114 for tripling and the Rule of 144 for quadrupling. Same idea, different number on top, since each multiple needs more compounding time.
Does the Rule of 72 work for very high or very low rates?
It is most accurate between about 5% and 12%. Above 20% or below 3% the shortcut drifts, so the exact compound formula is worth using there.
Should I use 72 or the precise number?
For mental math, 72 is fine. Some people nudge it to 70 for low rates and 73 or 74 for high rates, but for a quick estimate the difference rarely matters.
Last reviewed June 2026. This tool is for education, not financial advice.