Percentage Difference Calculator
Compare two values when neither is a clear starting point. Percentage difference measures their gap relative to their average.
Enter values to calculate.
How to calculate
Percentage difference compares two values with neither treated as the 'before' state: (|a − b| ÷ ((a + b) ÷ 2)) × 100. It's the right formula when you're comparing two independent measurements — two prices, two survey results, two lab readings — rather than tracking one value's change over time.
By hand, take the absolute value of the gap between the two numbers, then divide by their average (not either number alone), then multiply by 100. Comparing 8 and 12: the gap is 4, the average is 10, so 4 ÷ 10 × 100 = 40%.
Because it uses the average of both numbers as the denominator, percentage difference is symmetric — swapping the two values gives the same result, unlike percentage change or increase, which depend on which value came first. This also means percentage difference can never reach 200%, since the maximum gap relative to the average of two positive numbers is bounded.
Examples
- Between 10 and 20: (|10 − 20| ÷ 15) × 100 ≈ 66.67%.
- Between 40 and 50: (|40 − 50| ÷ 45) × 100 ≈ 22.22%.
- Between 6 and 14: (|6 − 14| ÷ 10) × 100 = 80%.
- Between 90 and 110: (|90 − 110| ÷ 100) × 100 = 20%.
Frequently asked questions
- What is the difference between percentage change and percentage difference?
- Percentage change compares a new value to a specific original value. Percentage difference compares two values relative to their average, with no fixed starting point.
- Does the order of the two numbers matter?
- No. Percentage difference uses the average of the two numbers, so swapping them gives the same result.
- Can percentage difference be negative?
- No. Percentage difference always uses the absolute value of the gap between the two numbers, so the result is zero or positive — it never reports direction. If you need to know which value is larger and by how much in relative terms, use percentage change instead, which keeps a sign.
- What's the highest percentage difference two numbers can have?
- For two positive numbers, percentage difference approaches but never reaches 200% — that happens as one value shrinks toward zero while the other stays fixed. For example, comparing 1 and 199 gives (|1 − 199| ÷ 100) × 100 = 198%, since the average of the two barely grows past half of the larger number.