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Percentage Calculator

Calculate percentages, percentage change, and what percent one number is of another with step-by-step breakdowns.

How to Use Percentage Calculator

  1. 1

    Enter your values

    Type the numbers you want to calculate percentages for.

  2. 2

    Choose calculation type

    Select percentage of, increase, decrease, or difference.

  3. 3

    View the result

    See the calculated percentage or resulting value instantly.

Tested tool guide Math and conversion tools Checked July 30, 2026

What Percentage Calculator does, with a checked example

This calculator covers three questions that use similar words but different formulas: finding a percentage of a number, finding what percentage one value is of another, and measuring percentage change from an old value to a new value. Each mode labels the inputs so the denominator remains visible.

Worked example

A concrete input and expected output from the current implementation.

Input

What is 25% of 80?

Expected output

20

Twenty-five percent is 25 divided by 100. Multiplying 0.25 by 80 gives 20.

How the result is produced

1

A percentage is a ratio per one hundred

For X percent of Y, the calculator uses X / 100 x Y. For X as a percentage of Y, it uses X / Y x 100 and requires Y to be nonzero.

2

Change uses the starting value as denominator

Percentage change is new minus old, divided by the absolute old value, times 100. The tool reports increase, decrease, or no change and rejects a zero starting value.

Good uses

  • Calculate a discount amount before subtracting it from a price.
  • Express one count as a share of a total.
  • Compare a measurement with its earlier value.

Limits and checks

  • Percentage points and percent change are not interchangeable.
  • A change from zero has no finite percentage in this formula.
  • Round only after the calculation when precision matters.

Common questions

What is the difference between 10% and 10 percentage points?

Moving from 20% to 30% is an increase of 10 percentage points but a 50% relative increase because 10 is half of the starting 20.

Why does reversing old and new change the result?

The starting value is the denominator. An increase from 80 to 100 is 25%, while a decrease from 100 to 80 is 20%.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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