Rule of 70

The Rule of 70 is a mathematical approximation used to estimate the time it takes for a quantity to double given a constant growth rate. It states that the doubling time (in years) is approximately 70 divided by the annual growth rate percentage. This rule is commonly applied in finance, economics, and population studies to quickly gauge exponential growth effects.

Also known as: Rule of 72, Rule of 69, Doubling Time Rule, 70 Rule, Growth Approximation Rule

Why learn Rule of 70?

Developers should learn the Rule of 70 when working with systems involving exponential growth, such as compound interest calculations, user base projections, or performance scaling in distributed systems. It provides a quick mental shortcut for estimating doubling times without complex calculations, useful in back-of-the-envelope analysis for business logic or resource planning.

Learning Resources

• docs: Investopedia: Rule of 70
• video: Khan Academy: Rule of 70 for Exponential Growth
• tutorial: Corporate Finance Institute: Rule of 70 Explained
• docs: Wikipedia: Rule of 72