Compare two estimates
How different are estimates of 80 and 100?
The difference is 20 and the average is 90. 20 ÷ 90 × 100 ≈ 22.22%, rounded to two decimal places. Swapping the two inputs gives the same answer.
About 22.22%
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Percentage difference calculator
Use the symmetric percentage-difference formula for measurements, estimates, experiments, and two values with equal status.
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Percentage difference22.222222%
|80 − 100| ÷ ((|80| + |100|) ÷ 2) × 100
Absolute difference20
Compare two values without choosing a starting value
Percentage difference treats both values equally. It divides their absolute difference by the average of their absolute values.
Compare two measurements
What is the percentage difference between 98 and 102?
The difference is 4 and the average is 100, so 4 ÷ 100 × 100 = 4%. Neither measurement is treated as the original or correct value.
4%
One of the values is zero
What is the percentage difference between 0 and 50?
The absolute difference is 50 and the average is 25. 50 ÷ 25 × 100 = 200%. With two zeros, the average would also be zero and the formula would be undefined.
200%
Change and difference answer different questions
A change from 80 to 100 is 25% because 80 is the starting value. The symmetric difference between 80 and 100 is about 22.22% because the reference is their average.
Calculate percentage change from an original valueUse the same units and meaning
Compare like-for-like values in the same units. This calculator uses absolute values in the average, including for negative inputs; check that this convention fits the comparison you need.
From question to answer in three moves.
01
Enter the first value.
02
Enter the second value.
03
See the absolute difference divided by the average magnitude of both values.
FORMULA & LIMITS
The calculation is visible, not a black box.
This symmetric comparison uses the average of absolute values, not a starting value. Two zeros have no defined percentage difference. Opposite signs give 200%; an absolute difference outside the numeric range is shown as undefined.
Formula useddifference % = |a − b| ÷ ((|a| + |b|) ÷ 2) × 100
Calculation checks updated 27 September 2026: automated tests cover sample inputs and numeric boundaries, not every possible input or commercial rule.
CLEAR ANSWERS
Math without mystery.
How is percentage difference calculated?+
Take the absolute difference between the two values, divide it by the average of their absolute values, then multiply by 100.
How is this different from percentage change?+
Percentage change uses an original value as the base. Percentage difference treats both values symmetrically, so swapping them does not change the answer.
What happens when both values are zero?+
The standard formula is undefined because its average denominator is zero.