Case 1
- First value
- 40
- Second value
- 60
40.0000%
Open with these valuesPercentage Difference Calculator
40.0000%
Result: 40.0000 %Percentage difference compares two values where neither is the reference: it divides their gap by their average, not by one of them. That makes it symmetric — swapping the two inputs changes nothing. When one value is a known correct one, use percent error instead.
The numbers at a glance
Held fixed: First value 40.0000.
| Second value | Result (%) |
|---|---|
| 0.0000 | 200.0000 |
| 20.0000 | 66.6667 |
| 40.0000 | 0.0000 |
| 60.0000Your value | 40.0000 |
| 80.0000 | 66.6667 |
| 100.0000 | 85.7143 |
| 120.0000 | 100.0000 |
Worked examples
Case 2
- First value
- 100
- Second value
- 50
66.6667%
Open with these valuesCase 3
- First value
- 5
- Second value
- 15
100.0000%
Open with these valuesHow it's calculated
%diff = |a − b| ÷ ((a + b) ÷ 2) × 100
- StepSubtract one value from the other and drop the minus sign.
- StepAdd both values and halve the sum to get their average.
- ResultDivide the gap by the average and multiply by 100.
What this number means
The denominator is the average of the two values
Neither value is the reference, so the gap is divided by their average. For 100 and 50 that gap is 50 and the average 75, giving 66.6667 % — dividing by 100 would give 50 %, dividing by 50 would give 100 %.
Symmetric, so the order never matters
The gap does not depend on the order and the average is the same either way. Comparing 40 with 60 gives 40 %, and so does comparing 60 with 40.
An average of zero has no answer
Values equal in size but opposite in sign, such as 5 and −5, average to zero and the formula divides by zero. The page shows no result rather than an infinite one.
The formula stands verbatim in the source
Math is Fun gives it as (25 − 15) ÷ ((25 + 15)/2) × 100 % = 50 %, together with the reason for taking the average. Checked on 2026-08-25.
Commonly misread
The gap is divided by one of the two values.
It is divided by their average: 100 and 50 come to 66.6667 %, where dividing by 100 would give 50 % and dividing by 50 would give 100 %.
Percentage difference and percent error are the same measure.
Percent error measures a reading against a value already known to be right. Percentage difference treats both values as equally valid.
40 and 60 sit further apart in percentage terms than 8 and 12.
Both pairs come to 40 %. What counts is the gap relative to the average, not the size of the numbers.
5 and −5 are as far apart as it gets, so the answer is large.
Their average is zero, so the measure is undefined and the calculator returns nothing at all.
Reference table
| Both values | Comparison | Percentage difference |
|---|---|---|
| 10, 10 | Identical readings | 0.0000 |
| 8, 12 | Same ratio as 40 and 60, smaller numbers | 40.0000 |
| 40, 60 | Average 50, gap 20 | 40.0000 |
| 100, 50 | One is double the other | 66.6667 |
| 5, 15 | One is triple the other | 100.0000 |
Questions
How do I calculate percentage difference?
Take the absolute gap between the two values, divide it by their average and multiply by 100. For 40 and 60 the gap is 20 and the average is 50, so 20 ÷ 50 × 100 = 40 %.
What is the difference between percentage difference and percentage change?
Percentage change is directional: it measures how far a value moved from an old reference to a new one, so it needs a before and an after. Percentage difference is symmetric and compares two values of equal standing, dividing by their average. Use change for growth over time and difference for two independent measurements.
Does the order of the two values matter?
No, the measure is symmetric, so swapping the first and second value gives exactly the same answer. The gap does not depend on the order, and the average is the same either way. Comparing 40 with 60 gives 40 %, and so does comparing 60 with 40.
When is the percentage difference undefined?
When the average of the two values is zero, the formula divides by zero and there is no answer. That happens whenever the values are equal in size but opposite in sign, for example 5 and −5. The calculator shows no result rather than an infinite one.
When should I use percentage difference?
Use it when neither value is the correct baseline: two lab readings of the same quantity, prices from two shops, or results from two methods. Because it treats both values equally, it is the fair way to say how far apart two figures of the same standing are.
Sources and last check
Information, not professional advice.