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Rule of 72 Calculator
How long it takes for money to double at a given return.
Enter values to see your result
Frequently asked questions
How accurate is the Rule of 72?
Very close for rates 6–10%. At 8%, Rule of 72 says 9 years; exact is 9.01 years. At 20%, Rule of 72 says 3.6 years; exact is 3.8 years.
Where does 72 come from?
Mathematical approximation of ln(2) × 100 ≈ 69.3. The number 72 is chosen because it divides cleanly by 1, 2, 3, 4, 6, 8, 9, 12 — making mental math easy.
Can I use it for inflation?
Yes — at 6% inflation, prices double in ~12 years. It's a quick way to visualise purchasing power erosion.
Rule of 115 for tripling?
Yes — 115 / rate gives years to triple. Rule of 144 gives years to quadruple.