Topic summary
Rule of 70
Extracted from the Wikipedia article Rule of 72.
In finance, therule of 72, therule of 70 and therule of 69.3 are methods for estimating an investment's doubling time. The rule number (e.g., 72) is divided by the interest percentage per period (usually years) to obtain the approximate number of periods required for doubling. Although scientific calculators and spreadsheet programs have functions to find the accurate doubling time, the rules are useful for mental calculations or when only a basic calculator is available.