The Rule Of 72 Calculator
The rule of 72 is a mental shortcut for doubling time: divide 72 by the annual return and you get roughly how many years it takes for money to double. It is fast, memorable and close enough for nearly every rate you will meet.
Doubling time (rule of 72)
9
- Exact doubling time
- 9.0065
- Value of 1,000 after that time
- $2,000.00
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
Doubling time = 72 / annual return percent
- rate
- Annual return as a percentage, such as 8 for 8%
- 72
- The magic numerator that makes the estimate work
- years
- Approximate years needed to double
How to check the result by hand
- 1
Identify the annual return
Use the net return after fees and, if relevant, after tax. An 8% gross return with a 1% fee is 7% for this purpose.
- 2
Divide 72 by the rate
72 divided by 8 is 9, so money doubles in about 9 years at 8%.
- 3
Check the range
The estimate is tightest between 6% and 10%. Outside that range, treat it as a rough guide and compute the exact figure if precision matters.
- 4
Compare with the exact answer
For confirmation, divide the natural log of two by the natural log of one plus the rate. The two should agree closely at ordinary returns.
- 5
Apply it to the outcome you care about
Use the rule on inflation, debt or savings to see how long the quantity takes to double, which is often more intuitive than an annual percentage.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate The Rule Of 72 page.