Percentage Calculator: Percent of, Change and Difference

Free calculator · clear working

Find a percentage of a number, express one number as a percentage of another, or calculate percentage change and percentage difference. Each mode shows its own formula and substitution.

Go to the calculator ↓

Runs in your browser. No account needed. Calculator inputs stay on this page and are not sent to a calculation server.

Use the Percentage Calculator

How to use this calculator

Choose the calculation first, then enter A and B exactly as described in the selection. Change uses A as the starting value. The change formula uses the absolute starting value so that the sign describes the direction of the numerical change.

Formula and method

Percent of: (A ÷ 100) × B. Percent ratio: (A ÷ B) × 100. Percentage change: [(B − A) ÷ |A|] × 100. Symmetric percentage difference for nonnegative values: |A − B| ÷ [(A + B) ÷ 2] × 100.

Worked example

20% of 150 is 30. An increase from 80 to 100 is 25%, because the increase of 20 is divided by the starting value of 80. The symmetric percentage difference between 80 and 100 is about 22.22%.

Assumptions and limits

A percent ratio needs a nonzero B. Percentage change from zero is undefined. Percentage difference is restricted to nonnegative values and is undefined when both values are zero. Percent change with negative starting values has competing conventions; the formula used here is displayed explicitly.

Common questions

Related calculators

Method reference: OpenStax textbook. Formula and tool checked October 31, 2026. Results are rounded for display.