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Percentage calculator

Calculate percentages, percentage values and change rates.

Use tool

CalculateAB

How to use it

Choose among three common percentage calculations: “A is what percent of B,” “A% of B,” or “percentage change from A to B.” The same two inputs have different meanings depending on the selected mode.

Choose the calculation mode.
Enter A and B.
Run the calculation and interpret the result using the selected formula.

A as % of B: A ÷ B × 100
A% of B: B × A ÷ 100
Change A→B: (B − A) ÷ A × 100
Zero restriction: the denominator B or A must not be zero

A=25 and B=100 produces different answers by mode

“A is what percent of B” gives 25%; “A% of B” gives 25; “change from A to B” means 25→100, which is +300%.

“Increased by 300%” and “became 300% of the original” are different statements. Moving from 25 to 100 reaches 400% of the original level, but the increase itself is 300%.

The denominator decides what the percentage means

A/B and B/A are not interchangeable. Decide which quantity is the reference before choosing the mode.

Percentage change uses the original A as the base

100→120 is +20%, while 120→100 is about −16.67%. Reversing a change does not produce an equal opposite percentage.

Negative values are calculated mathematically

The inputs are not restricted to positive numbers. For real-world quantities that cannot logically be negative, make sure the entered values still make sense.

Displayed rounding is only presentation

Percentage results are shown to a practical number of decimal places and unnecessary trailing zeros are removed; the underlying formula remains the same.

Use percentage points for changes between percentages when appropriate

Moving a rate from 20% to 25% is +5 percentage points, while its relative percentage increase is 25%. Choose the wording that matches the question.

Related references: SI prefixes & units · Number formats · Cooking measures