Percentage Calculator

Calculate discounts, tips, VAT, percentage change, and percentage difference. Results update as you type.

Percentage Difference Calculator

Compare two numbers and see how far apart they are, expressed as a percentage of their average. Unlike percentage change, this is symmetric: swapping the two inputs gives the same answer. Use it to compare two prices for the same item, two measurements, or two competing estimates, anywhere there's no natural "before" and "after".

Difference betweenand?
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How percentage difference is calculated

The formula is |a − b| ÷ ((a + b) ÷ 2) × 100. The numerator is the absolute distance between the two numbers; the denominator is their mean. Because the operation uses absolute value and a symmetric average, the order of inputs doesn't matter.

Both numbers must be non-zero (and not opposite signs that average to zero), otherwise the average is zero and the result is undefined. The calculator shows an undefined indicator in that case.

Worked example

Two stores list the same chair at $80 and $120. Enter 80 and 120. The mean is 100, the absolute difference is 40, so the percentage difference is 40%. Either order produces the same answer.

Percentage Difference Calculator FAQ

What's the formula?
|a − b| ÷ ((a + b) ÷ 2) × 100. Absolute value in the numerator, arithmetic mean in the denominator.
Difference or change: which should I use?
Use percentage change when one value comes before the other (last quarter vs. this quarter, before vs. after). Use percentage difference when the two values are peers: two estimates, two prices, two measurements. The numbers will not be the same. See the percentage change calculator for the directional version.
Why does the result show "Undefined" sometimes?
When both values are zero, the average is zero and the formula divides by zero. Some pairs of opposite-sign values can also average to zero (e.g. -5 and 5). In those cases there's no defined percentage difference.
Does the order of inputs matter?
No. (80, 120) and (120, 80) give the same answer because of the absolute value in the formula. This is the main practical distinction from percentage change.
Can the result be negative?
No. Percentage difference uses an absolute value, so it's always zero or positive. If you need a signed answer, you want percentage change instead.

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