Why 70 instead of 72?

Both are approximations of ln(2)×100 ≈ 69.3; 70 divides more evenly by common growth rates like 5, 7, and 10, while 72 divides more evenly by 6, 8, 9, and 12.

Rule of 70 Calculator

The Rule of 70 is an alternative to the Rule of 72 for quickly estimating how long it takes a growing quantity to double, commonly used in economics for GDP or population growth.

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Years to Double: 8.75

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Formula

Years to Double ≈ 70 / Growth Rate

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