The Rule of 70: A Simple Shortcut to Calculate Exponential Growth

The Rule of 70 is a straightforward mathematical tool for estimating how long it takes for a growing variable to double. By dividing 70 by the annual growth rate, you can bypass complex calculations to understand the impact of compounding in finance, business, and biology.

This method provides a quick approximation for any value increasing at a steady percentage rate. Whether you are tracking the growth of an investment account, a nation's GDP, startup user acquisition, or even bacterial reproduction, the formula remains consistent: divide 70 by the growth rate percentage to find the doubling time.

Beyond simple projections, the rule can also be applied in reverse to determine necessary growth rates. It serves as a practical mental model for visualizing the power of compounding without needing to perform the full, tedious arithmetic required for exponential growth equations.

Source: What Is the Rule of 70?