How to Calculate Percentages (Step-by-Step Guide)

Percentages compare a value to 100. Here are the three core formulas with examples and quick tools.

1) Percent of a number

Formula: (% × base) ÷ 100. Example: 18% of 250 = 45. Try it in the percent of calculator.

2) What percent is A of B?

Formula: (A ÷ B) × 100. Example: 25 is what percent of 80? 31.25%. Use the what percent tool.

3) Percent change

Formula: ((new − old) ÷ old) × 100. Example: from 50 to 70 = 40% increase. Try the percent change calculator.

Tip: Avoid dividing by zero; ensure the “whole” is not 0.