Rule of 72 Calculator
Estimate years to double money at a fixed rate.
Enter the values and press Calculate.
How to use Rule of 72 Calculator
The rule of 72 is a quick mental shortcut for doubling time. This tool applies it exactly so you can plan savings or debt payoff.
Open Rule of 72 Calculator on toolpermarket. It runs entirely in your browser, so you can start without creating an account.
Enter the annual interest rate in the fields above, then press Calculate.
Read the result below the form. Change any input and run it again as many times as you like — the math is instant and local.
Worked example. At 8 percent a year, money doubles in about 72 divided by 8, which is 9 years.
When to use Rule of 72 Calculator. Use it to compare investments, loans, or inflation and see how fast a balance grows or shrinks.
Frequently asked questions
Is Rule of 72 Calculator free to use?
Yes. Rule of 72 Calculator runs entirely in your browser. There is no account, no upload, and no cost.
Does Rule of 72 Calculator work on mobile?
Yes. The layout is responsive, so Rule of 72 Calculator works on any phone, tablet, or desktop with a modern browser.
Why does the rule of 72 work?
It approximates the natural logarithm math of compounding. Dividing 72 by the rate gives a close estimate of doubling time for rates roughly between 2 and 15 percent.
Is the result exact?
It is an approximation, not a precise compounding figure. This tool shows the rule-of-72 estimate; for exact growth use a future value calculator.