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Rule of 72 Calculator
Enter a yearly rate of return. You get the doubling time from the rule of 72 next to the exact figure, and the time to triple.
| Rate | Rule of 72 | Exact |
|---|---|---|
| 2% | 36.0 years | 35.0 years |
| 4% | 18.0 years | 17.7 years |
| 6% | 12.0 years | 11.9 years |
| 8% | 9.0 years | 9.0 years |
| 10% | 7.2 years | 7.3 years |
| 12% | 6.0 years | 6.1 years |
Example
At 7% a year the rule of 72 gives 10.3 years to double. The exact answer is 10.24 years, so $10,000 becomes $20,000 in a little over a decade.
How the rule of 72 calculator works
The rule of 72 is a shortcut: years to double = 72 / rate. At 6% money doubles in about 12 years, and at 9% in about 8.
The exact formula is ln(2) / ln(1 + rate). The shortcut works because ln(2) is about 0.693 and 72 has many divisors, which makes the mental arithmetic easy.
It is most accurate between about 5% and 10%. At very high rates it underestimates the time, as the table shows.
Common questions
Does the rule of 72 work for inflation and debt?
Yes. Divide 72 by the inflation rate to see how long prices take to double, or by a loan’s interest rate to see how fast an unpaid debt doubles.
Is there a rule for tripling money?
Roughly, divide 114 by the rate. For quadrupling, the money doubles twice, so use twice the doubling time.
Does it include regular contributions?
No. It applies to a single amount left to grow. Use the compound interest calculator to include monthly contributions.