A percentage difference calculator answers a specific kind of question: when two values are being compared and neither one is treated as the "original" or the "starting point," how far apart are they, expressed as a percentage? This is different from percentage increase or decrease, both of which assume a direction — a before and an after. Percentage difference has no direction; it simply measures how far apart two numbers are relative to their average. For a part-to-whole percentage instead, use the percentage calculator.
This page explains what percentage difference actually means, walks through the percent difference formula step by step, and covers several worked examples showing how to calculate percent difference between real numbers. A working calculator is available above for anyone who wants the instant result. Browse all calculators if you need a different tool.
What Is Percentage Difference?
Why Percentage Difference Is Symmetrical
Percentage difference exists for situations where two values are being compared as equals — two lab measurements, two competing prices, two survey results — with neither one designated as the "before" value. Because of that, the formula is built around the average of the two numbers rather than treating one as a fixed starting point. This is what makes percentage difference symmetrical: comparing A to B gives the same result as comparing B to A, which is not true of percentage increase or percentage decrease.
The Percent Difference Formula Explained
The Formula Itself
Percentage Difference = (|A − B| ÷ ((A + B) ÷ 2)) × 100
Breaking this down: subtract the two values and take the absolute value (ignoring which one is larger), divide that by the average of the two values, then multiply by 100. Using the average in the denominator — rather than one specific value — is exactly what keeps the result symmetrical regardless of which number is entered first.
This is the exact percent difference formula behind every result this calculator produces, and it directly answers how to calculate percent difference for any pair of numbers.
How to Calculate Percent Difference: Worked Examples
Example: Comparing 40 and 60
|40 − 60| = 20
(40 + 60) ÷ 2 = 50
20 ÷ 50 = 0.40
0.40 × 100 = 40% difference
The percentage difference between 40 and 60 is 40%.
Example: Comparing Two Test Scores, 72 and 78
|72 − 78| = 6
(72 + 78) ÷ 2 = 75
6 ÷ 75 = 0.08
0.08 × 100 = 8% difference
Two test scores of 72 and 78 have an 8% percentage difference between them.
Example: Comparing Product Prices, $120 and $135
|120 − 135| = 15
(120 + 135) ÷ 2 = 127.5
15 ÷ 127.5 = 0.1176
0.1176 × 100 = 11.76% difference
Two competing prices of $120 and $135 differ by approximately 11.76% — a useful figure when comparing quotes or offers without treating either one as the "original" price.
How to Calculate Percentage Difference Between Two Figures Step by Step
For anyone working through this by hand rather than using the calculator above, the full process for how to calculate percentage difference between two figures breaks down into four steps:
- Find the absolute difference between the two numbers (subtract the smaller from the larger, or just ignore the sign of the result).
- Find the average of the two numbers (add them together, divide by 2).
- Divide the absolute difference by that average.
- Multiply the result by 100 to express it as a percentage.
Following these four steps in order will produce the correct percent difference for any two positive numbers, regardless of which one is larger or which one was entered first.
Percentage Difference vs. Percentage Increase/Decrease — Key Distinction
This is the single most important thing to understand before using any percentage comparison tool: percentage difference and percentage increase/decrease are not interchangeable, and using the wrong one produces a technically correct but contextually wrong answer.
Percentage increase/decrease assumes direction. There's a clear starting value and a clear ending value, and the calculation measures growth or decline relative to that starting point. A price moving from $50 to $60 is a 20% increase — but the reverse, $60 back down to $50, is not a 20% decrease, it's a 16.67% decrease, because the formula divides by a different starting value each time.
Percentage difference has no direction. It doesn't matter which number came first — comparing $50 to $60 gives exactly the same percentage difference as comparing $60 to $50, because both calculations divide by the shared average rather than by one specific starting value.
If the question involves something changing over time — a price rising, a population growing, a metric shrinking — the percentage increase or percentage decrease calculator is the correct tool. If the question is simply "how far apart are these two numbers," this percentage difference calculator is the right one.
Where This Calculator Is Useful
Science & Lab Measurements
Comparing two experimental measurements or two instrument readings of the same quantity, where neither reading is the "correct" or "original" value — percentage difference is the standard way this comparison is reported in scientific contexts.
Comparing Prices or Quotes
Comparing two competing prices, quotes, or offers side by side, without implying that either one is the baseline the other changed from.
Statistical & Data Comparisons
Comparing two data points, survey results, or benchmark figures where the goal is understanding how far apart they are, not which one came "before" the other.
Common Mistakes to Avoid
Using percentage difference when percentage change was actually needed. If there's a genuine "before and after" relationship, percentage increase or decrease is the correct calculation — using percentage difference instead will understate or overstate the change depending on the direction.
Forgetting to use the average, not one of the two values. A common manual error is dividing by one of the two numbers instead of their average, which breaks the symmetry that defines percentage difference and produces two different answers depending on which number is treated as the divisor.
Ignoring the absolute value step. Since percentage difference is always expressed as a positive number, the subtraction step should ignore which value is larger — the formula measures distance apart, not direction.
Frequently Asked Questions
How do I calculate percent difference?
Find the absolute difference between the two numbers, divide it by their average, then multiply by 100. For example, the percentage difference between 40 and 60 is (20 divided by 50) times 100, which equals 40%.
What's the percent difference formula?
Percentage Difference equals the absolute value of A minus B, divided by the average of A and B, multiplied by 100.
How is percentage difference different from percentage change?
Percentage difference is symmetrical and does not assume a direction, so comparing A to B gives the same result as comparing B to A. Percentage change, whether increase or decrease, assumes a starting value and an ending value, and the result depends on which number came first.
How do I calculate percentage difference between two figures like 120 and 135?
Subtract the smaller from the larger to get 15, find their average of 127.5, divide 15 by 127.5, then multiply by 100, resulting in approximately 11.76%.
Can percentage difference be negative?
No. Because the formula uses the absolute value of the difference, percentage difference is always expressed as a positive number.
When should I use percentage difference instead of percentage increase or decrease?
Use percentage difference when comparing two independent values with no assumed direction, like two measurements or two competing prices. Use percentage increase or decrease when there is a clear before-and-after relationship, like a price rising or a population shrinking over time.
Does it matter which number I enter first?
No. Because the formula is based on the average of both numbers rather than one specific starting value, the result is the same regardless of the order the two numbers are entered in.
Is this percentage difference calculator free to use?
Yes. It is free, requires no sign-up, and returns results instantly as values are entered.