Percentage Difference Calculator
Compare two values as a percentage difference.
Results update as you type.
How it works
Percentage difference measures how far apart two values are relative to their typical size, without labelling either one as the reference point. Instead of asking how much A grew into B, it treats the two numbers even-handedly: it takes the absolute gap between them and compares it against their average. That symmetry is the defining trait, so the percentage difference calculator returns the same answer whether you enter 40 then 60 or 60 then 40, because swapping them changes neither the gap nor the average. The method matters when there is no natural before or after. Comparing two lab measurements, two suppliers' prices or two sensor readings, you rarely want one to count as the baseline; dividing by the average rather than by either value keeps the comparison neutral. For 40 and 60 the gap is 20, the average is 50, and 20 over 50 is a 40% difference. A percentage difference calculator applies that consistently and always reports a non-negative figure. Engineers, scientists, accountants and quality analysts reach for this percentage difference calculator when they need an unbiased comparison of two equal-standing quantities rather than a directional change from a fixed origin.
difference (%) = (|a − b| ÷ ((a + b) ÷ 2)) × 100
Taking the absolute difference measures how far apart the two values are while discarding which one is larger, so the result stays positive. Dividing by their average, not by either value, is what keeps the comparison symmetric, because the average treats both numbers equally. Multiplying by 100 states the gap as a percent. For 40 and 60, a gap of 20 over an average of 50 gives 40%.
Source:Standard arithmetic
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter first value and second value.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Percentage difference updates instantly as you type — no button to press.
Frequently asked questions
What is percentage difference?
Percentage difference is the gap between two values expressed as a percentage of their average. It compares two numbers that stand on equal footing, with neither treated as the original or the reference. Because it divides by the average of the pair, it is symmetric: the values 40 and 60 differ by 40% no matter which you list first, and the answer is always zero or positive.
How is percentage difference different from percentage change?
Percentage change divides by the original value and has a direction, so it tells you how much one number grew or shrank into another. Percentage difference divides by the average of the two values and has no direction, so it simply measures how far apart they are. Change suits before-and-after comparisons; difference suits two readings where neither is the starting point.
When should I use percentage difference?
Use it whenever the two values you are comparing have no natural order: two independent measurements, two competing quotes, two instruments reading the same thing. In those cases picking one as the baseline would bias the result, so dividing by the average keeps the comparison fair. If one number is clearly a before and the other an after, percentage change is the better fit instead.
Can percentage difference be negative?
No. The formula uses the absolute value of the gap between the two numbers, which strips away any sign, so the result is always zero or positive. A difference of zero means the values are identical. This is a deliberate consequence of the method being symmetric: since neither value is treated as the baseline, there is no direction for the figure to point, and therefore no negative outcome.
How do I find the percentage difference between two numbers?
Subtract the smaller value from the larger to get the absolute gap, add the two numbers and halve them to get the average, then divide the gap by the average and multiply by 100. For 40 and 60, the gap is 20 and the average is 50, so 20 divided by 50 times 100 is a 40% difference. The order you enter the two numbers never affects the outcome.