How to use this calculator
There is one input: the yearly rate of return, as a percent. Enter the rate you want to test, and the calculator returns four figures.
- Years to double by the rule of 72: the quick mental-math estimate.
- Exact years to double: the precise answer using compound growth.
- Years to triple: how long until the money is three times the starting amount.
- Years to grow tenfold: how long until it is ten times the starting amount.
The starting amount does not matter. At a given rate, $100 and $100,000 take the same time to double. The results assume the rate stays the same, growth is compounded once a year, and nothing is added or withdrawn.
Worked example
These are the starting values in the calculator above and the results they give. Change any input to see your own numbers.
- Yearly rate of return
- 7%
- Years to double
- 10.3 years
- Exact years to double
- 10.2 years
- Years to triple
- 16.2 years
- Years to grow tenfold
- 34 years
How the rule of 72 is calculated
The rule of 72 is a shortcut: divide 72 by the yearly rate, written as a whole number, to estimate the years needed to double. At 8% a year, 72 ÷ 8 = 9 years. At 3% a year, 72 ÷ 3 = 24 years.
The exact figure comes from the compound growth formula. It uses logarithms, which is why the shortcut exists: 72 is easy to divide in your head. The number 72 is used because it gives close answers at everyday rates and divides evenly by 2, 3, 4, 6, 8, 9 and 12.
Tripling and tenfold growth use the same exact method with a target of 3 or 10 instead of 2. Read more in the rule of 72 guide.
Rule of 72: T = 72 ÷ R. Exact: T = ln(2) ÷ ln(1 + r)- T
- years to double
- R
- yearly rate of return as a percent (for example 6)
- r
- yearly rate of return as a decimal (for example 0.06)
- ln
- natural logarithm; use ln(3) to triple and ln(10) for tenfold
How to read the results
Compare the two doubling figures to see how close the shortcut is. The rule of 72 is most accurate for rates in the high single digits. At very low rates it slightly overstates the time, and at high rates it understates it. For rough planning, the gap is usually too small to matter.
Some useful ways to apply it:
- Run it backward. Divide 72 by a number of years to estimate the rate needed to double in that time. Doubling in 12 years takes about 72 ÷ 12 = 6% a year.
- Use it for costs. The rule works for anything that compounds. Divide 72 by an inflation rate to see how long prices take to double, or by a debt's interest rate to see how fast an unpaid balance could double.
- Notice the pattern. Tripling does not take one and a half times as long as doubling, and tenfold growth takes a little more than three doublings. Growth builds on itself.
To see a full balance over time with regular deposits, use the compound interest calculator.
Frequently asked questions
What is the rule of 72?
The rule of 72 is a quick way to estimate how long it takes for money to double at a fixed yearly rate of return. You divide 72 by the rate. At 6% a year, the estimate is 72 ÷ 6 = 12 years. It works because of how compound growth behaves, and it needs no calculator.
How accurate is the rule of 72?
It is close for common rates and best around 8% a year, where the estimate nearly matches the exact answer. As the rate moves far above or below that, the error grows. At very low rates it gives a slightly longer time than the true figure, and at high rates a shorter one. This calculator shows both so you can compare.
Why 72 and not another number?
The mathematically exact number for very low rates is closer to 69.3, which comes from the natural logarithm of 2. But 72 gives better answers at the rates people usually meet and has many whole-number divisors, so the division is easy to do in your head. Some people use 69 or 70 for low rates or continuous compounding.
Does the rule of 72 work for inflation and debt?
Yes. It applies to anything that grows at a steady compound rate. Divide 72 by the inflation rate to estimate how long prices take to double, which is also how long it takes money to lose half its buying power. Divide 72 by a loan's interest rate to see how fast an unpaid balance would double.
How long does it take to triple my money?
A common shortcut is the rule of 114: divide 114 by the yearly rate to estimate the years to triple. At 6% a year, that is 114 ÷ 6 = 19 years. The calculator shows the exact figure for tripling and for tenfold growth, based on compound growth at the rate you enter.
This calculator gives estimates for education only. It does not know your full situation and is not financial advice. Reviewed and updated November 15, 2026.