Percentage Difference Calculator

How to use

1. 1Type the first value into the First value field.
2. 2Type the second value into the Second value field. Decimals and negative numbers are allowed.
3. 3Read the percentage difference, shown with the worked formula so you can check it.
4. 4Use the cards below for the absolute difference, the average, and the percentage change in each direction.
5. 5Press Copy result to copy the answer, Swap to flip the two values, or Clear to start over.

About this tool

Percentage Difference Calculator finds how far apart two numbers are, expressed as a percentage of their average. It uses the symmetric percentage difference formula, the absolute difference between the two values divided by the average of their magnitudes, multiplied by 100: |a - b| / ((|a| + |b|) / 2) x 100. Because the denominator is the average of both values rather than one of them, the result is the same whichever order you enter the numbers, which is exactly what people mean when they ask for the percentage difference between two equal partners such as two measurements, two prices, or two readings where neither is a starting point. This is different from percentage change, which is directional and divides by the original value using (new - old) / old x 100, and from percent error, which divides the gap by a known true value. Those three are constantly confused, so this tool computes the symmetric percentage difference as the headline answer and then shows the absolute difference, the average of the two values, and both directional percentage changes side by side, so you can see all of the common interpretations at once and pick the one your question actually needs. The calculator accepts decimals and negative numbers, handles comma or point decimal entry, and explains the edge cases honestly: when both values are zero the percentage difference is undefined because the average is zero, and a directional percentage change is undefined whenever its starting value is zero. A short guide below the result spells out when to use percentage difference and when to use percentage change. Every calculation runs locally in your browser, so the numbers you enter are never uploaded or stored.

Free to use. Works in your browser. No signup, no login.