Rule of 72 Calculator
Enter a rate to see how quickly compound growth doubles, triples and quadruples your money.
How to use the Rule of 72 Calculator
- Enter the annual rate of return or interest.
- Read off how many years it takes to double your money.
- See the tripling and quadrupling times too.
- Try different rates to feel how much faster higher returns compound.
Years to double ≈ 72 ÷ rate · Triple ≈ 114 ÷ rate · Quadruple ≈ 144 ÷ rate
About the Rule of 72 Calculator
The Rule of 72 is the most useful piece of mental maths in personal finance. Divide 72 by an annual rate of return and you get, near enough, the number of years it takes money to double under compound growth. At 8% that is about nine years; at 6%, twelve. This calculator applies it instantly, and adds the companion rules — 114 for tripling and 144 for quadrupling — so you can see the whole compounding picture at a glance.
What makes it powerful is how it exposes the cost of small differences in rate. The gap between a 6% and an 8% return does not sound like much, but it is the difference between doubling in twelve years and in nine — and over a lifetime, several extra doublings. It also works in reverse as a gut check: if something promises to double your money in three years, that implies roughly a 24% annual return, which tells you how much risk must be involved.
It is an approximation, most accurate for rates in the 6–10% range and drifting a little at the extremes. For an exact figure with a starting sum and contributions, use the compound interest calculator or the future value calculator.
Frequently asked questions
How accurate is the Rule of 72?
Very close for rates between about 6% and 10%. At much higher or lower rates it drifts slightly from the exact answer, but it stays a reliable quick estimate. For precision, use a compound interest calculator.
Does it work for inflation too?
Yes. Divide 72 by an inflation rate to see how long it takes prices to double — or your money's buying power to halve. At 3% inflation, that is about 24 years.
Why 72?
72 is a convenient number that divides evenly by many rates (2, 3, 4, 6, 8, 9, 12) and closely matches the exact compounding maths in the common range of returns, which is why it became the standard rule of thumb.