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Percentage Calculator – Percent Of, Change, Difference & More

Percentages appear everywhere — tax rates, discounts, tip amounts, test scores, interest rates, salary changes, statistics — but different percentage questions need different formulas. 'What is 20% of 80?' is different from 'What percentage is 80 of 400?' which is different from 'What was the percentage increase from 80 to 100?'

This calculator handles every standard percentage calculation type. Select the calculation you need, enter your numbers, and see the result with the formula shown. No memorising formulas required.

How to use the Percentage Calculator

Select the type of percentage calculation.

Enter the values in the input fields shown.

View the result instantly with the formula that was applied.

Percentage Calculation Types & Formulas
Calculation	Formula	Example
X% of Y	(X ÷ 100) × Y	20% of 150 = 30
X is what % of Y	(X ÷ Y) × 100	45 is 75% of 60
Percentage increase	((New − Old) ÷ Old) × 100	80→100 = +25%
Percentage decrease	((Old − New) ÷ Old) × 100	100→75 = −25%
Percentage difference	(\|A−B\| ÷ avg(A,B)) × 100	80 vs 100 = 22.2%

Percentage Calculator FAQ

What is the difference between percentage change and percentage difference?

Percentage change compares a new value to a reference (original) value — direction matters (increase vs decrease). Percentage difference compares two values with no defined reference; it's symmetric and always positive.

How do I convert between decimals and percentages?

To convert percentage to decimal: divide by 100 (75% = 0.75). To convert decimal to percentage: multiply by 100 (0.35 = 35%).

What is percentage error?

Percentage error = (|measured − true| ÷ |true|) × 100. It measures how far a result deviates from the correct value.

Why do percentages in polls sometimes not add to 100%?

Rounding. When each percentage is rounded to the nearest whole number separately, the total can be 99% or 101%. This is called rounding error and is disclosed in reputable polling methodology.