Rule of 72 Calculator
Quickly estimate investment doubling time — or the rate needed — with the Rule of 72.
Not financial advice. The Rule of 72 is an approximation.
What is the Rule of 72?
The Rule of 72 is a simple mental-math shortcut for estimating how long it takes an investment to double at a fixed annual interest rate. Divide 72 by the annual rate (in percent) and you get the approximate number of years to double: Years = 72 ÷ Rate.
You can also flip it: if you know how many years you want to double your money, divide 72 by those years to find the required rate: Rate = 72 ÷ Years.
The rule is historically attributed to Luca Pacioli, the 15th-century Italian mathematician who also documented double-entry bookkeeping. It's an approximation — the exact formula uses the natural logarithm — but it's remarkably accurate for rates between 6% and 10%.
FAQ
How accurate is the Rule of 72? Very accurate for rates in the 6–10% range; it overestimates slightly at lower rates and underestimates at higher ones. For a 2% rate the rule gives 36 years, while the exact answer is about 35. For 20% it gives 3.6 years vs. the exact 3.8 years.
Is my data sent anywhere? No — all calculations happen locally in your browser. Nothing is uploaded to any server.