Learn How Percentages Work

These guides explain the arithmetic behind the calculators. Start with the three core operations, keep a formula sheet nearby, and use the disambiguation pages when two similar words mean different things.

Guides

Short explainers with worked examples and links to the matching tools.

How to calculate a percentage

Steps for percent of a number, what percent one number is of another, and percentage change.

Percentage formulas

A formula sheet for the main percentage operations, including Excel snippets.

Percentage vs percentile

Why 90% and the 90th percentile are not the same measurement.

Percentage points

Percent, percentage points, and basis points, with a worked increase example.

Common percentages

Mental-math values for 1%, 5%, 10%, 15%, 20%, 25%, and 50% of round numbers.