// by seankriegler.com
Rule of 72 Calculator
How many years to double your money at a given interest rate
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Rule of 72 (approx)
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Exact Years
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Doubled Value
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Quadrupled In
| Rate | 2% | 4% | 6% | 8% | 10% | 12% | 15% | 20% |
|---|---|---|---|---|---|---|---|---|
| Years | 36.0 | 18.0 | 12.0 | 9.0 | 7.2 | 6.0 | 4.8 | 3.6 |
// The Rule
Divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 8%: 72 ÷ 8 = 9 years. Simple, surprisingly accurate.
// Works Both Ways
The Rule of 72 also shows how fast inflation erodes purchasing power. At 6% inflation, your money's buying power halves in just 12 years.
// Quadrupling
To quadruple your money, simply double the doubling time. At 8%, you double in 9 years and quadruple in 18 years. Each doubling builds on the last.
// Why 72?
72 is used because it's easily divisible by many numbers (2, 3, 4, 6, 8, 9, 12). The mathematically exact number is ~69.3, but 72 is easier for mental math.