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Percentage: The Complete Guide for 2026

Learn how the Percentage Calculator works, what percent of, what percent, and percent change calculate, and when to use each.

Published August 28, 20264 min read
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What does the Percentage Calculator do?

The Percentage Calculator handles three common percent problems in one place: finding a percent of a number (percent of), finding what percent one number is of another (what percent), and measuring the change between two values (percent change).

Common uses

  • Percent of — work out discounts, tips, tax, or commissions, such as 15% of 80
  • What percent — express one quantity relative to another, like what percent 25 is of 200
  • Percent change — measure increases or decreases, such as a price rising from 40 to 50
  • Ratios — convert between percentages and ratios quickly

Key features

  • Percent of — calculates a given percentage of a number (part = percent × whole)
  • What percent — finds the percentage that one number represents of another (percent = part / whole × 100)
  • Percent change — computes the relative difference between an old and new value

How it works

The calculator applies the standard percent formulas:

  • Percent of: part = percent ÷ 100 × whole
  • What percent: percent = part ÷ whole × 100
  • Percent change: change = (new − old) ÷ old × 100

A positive percent change indicates an increase; a negative value indicates a decrease. The tool returns the numeric result instantly, so no manual math is needed.

Verdict

The Percentage Calculator covers the three percent problems you meet most often, with correct formulas every time. Open Percentage Calculator and get your answer in seconds.

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Frequently asked questions

How do you calculate percent of a number?

Multiply the percent (as a decimal) by the whole. For 15% of 80, that's 0.15 × 80 = 12.

How is percent change calculated?

Percent change = (new value − old value) ÷ old value × 100. A positive result is an increase; negative is a decrease.

What does "what percent" tell me?

It expresses one number as a percentage of another, using percent = part ÷ whole × 100.

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