Rule of 72 Calculator
Enter a rate and we estimate the years to double your money. Or enter a number of years and we find the rate you would need.
This calculator gives estimates for information only. It is not financial, tax or legal advice. Real results depend on lender terms, fees and local rules.
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The formula
Years to double = 72 / interest rate (%). Exact: ln(2) / ln(1 + rate).
How the rule works
Divide 72 by your annual return and you get roughly how many years it takes for your money to double. At 8 percent, 72 / 8 = 9 years. At 6 percent it is 12 years, and at 3 percent it is 24 years.
Why 72?
It is a convenient number that divides by many rates and fits the compounding maths well for rates around 6 to 10 percent. We also show the exact figure from the compound formula so you can see how close it is.
Use it in reverse
To double your money in 10 years you need about 72 / 10 = 7.2 percent a year. The rule also works for inflation: at 3 percent inflation, prices double in about 24 years.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| Years to double my money; Annual rate (%) or years: 8 | Years to double (rule of 72): 9 years |
| Years to double my money; Annual rate (%) or years: 6 | Years to double (rule of 72): 12 years |
| Rate needed to double in N years; Annual rate (%) or years: 10 | Rate needed (rule of 72): 7.2% a year |
| Years to double my money; Annual rate (%) or years: 3 | Years to double (rule of 72): 24 years |
Rule of 72 Calculator: frequently asked questions
Is the rule exact?
No, it is a quick estimate. It is closest for rates between about 6 and 10 percent.
Is this financial advice?
No. It gives an estimate from the numbers you enter. Real offers depend on fees, tax and the lender or provider, so check the terms before you commit.
Is what I enter in this calculator saved or sent anywhere?
No. The calculation runs in your browser, so what you enter is not sent to our servers. We only count, anonymously, whether a tool ran successfully.
Is this calculator free to use?
Yes. It is free, needs no sign-up and has no usage limit.
Last reviewed: October 3, 2026