Rule of 72 Calculator
Enter an interest rate to find how long any investment takes to double — or find the rate needed to double by a target date.
Common Doubling Times
Frequently Asked Questions
What is the Rule of 72?
Divide 72 by the annual interest rate to estimate the years needed to double money. At 6%: 72÷6=12 years. At 8%: 72÷8=9 years. It’s accurate within 1-2% for rates between 2-20%.
Can I use the Rule of 72 for debt and inflation?
Yes — it works in any direction. Credit card debt at 22% doubles in about 3.3 years. Inflation at 3% halves purchasing power in about 24 years. It’s one of the most useful mental math tools in finance.
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