Your inputs

Choose a calculation

Calculation type

Percentage

The percentage to take, such as 20.

Of this number

The number to take the percentage of.

Your inputs are calculated locally and are not stored.

Result50

20% of 250 is 50.

Formula used: Result = Value × (Percent ÷ 100)

Formula & methodology

How each percentage is calculated

Each mode uses a single, direct formula. “% of” multiplies a value by the percentage expressed as a decimal. “Change” measures the difference between a starting and an ending value relative to the size of the starting value. “What %” divides a part by a whole and scales it to a percentage. Because change and what-percent both divide by an input, the starting value and the whole must not be zero.

Percent of: Result = Value × (Percent ÷ 100)
Change: Change % = ((To − From) ÷ |From|) × 100
What percent: Result % = (Part ÷ Whole) × 100

Worked example

Three quick examples

% of: 20% of 250 is 250 × 0.20 = 50. Change: going from 50 to 80 is (80 − 50) ÷ 50 × 100 = a 60% increase, an absolute difference of 30. What %: 30 is (30 ÷ 120) × 100 = 25% of 120.

General-purpose estimate.

Assumptions

What this calculator assumes

Percentage change is measured against the absolute value of the starting number, so results stay intuitive with negative inputs.
The starting value (change) and the whole (what percent) must be non-zero, since dividing by zero is undefined.
Results are rounded for display; no rounding is applied mid-calculation.

Common questions

Percentage FAQ

What is the difference between percent of and what percent?

“% of” starts with a percentage and a number and returns an amount (20% of 250 is 50). “What %” starts with two numbers and returns the percentage one is of the other (30 is 25% of 120).

Why can’t the starting value be zero?

Percentage change divides by the starting value, and dividing by zero is undefined. If the original amount is zero, any increase is mathematically infinite, so the calculator asks for a non-zero starting value instead.

Primary source

Sources and review notes

Consumer Financial Protection Bureau — consumer tools and money-math basics

Methodology last checked Jul 14, 2026. Formula implementation is covered by deterministic unit tests.