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Percentage Difference Calculator
By: Conor Keenan, AWMA®
Editorial Independence: Our recommendations and reviews are our own. Partner commissions may help keep our site free and do not influence our editorial content.
Compare two values
Uses the absolute gap divided by the average magnitude of the two values. Swapping values gives the same result. Use the same units.
Result:
Percentage difference: 0.00%
Find how far apart two values are relative to their average size. Enter two numbers to calculate their percentage difference when neither is the starting value or a benchmark. For positive numbers, the calculator divides the absolute difference by their average, then multiplies by 100.
The result has no increase or decrease direction: swapping the two inputs gives the same answer. To measure movement from an original value to a new one, use the percentage change calculator.
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In This Article
Key Takeaways
- Percentage difference compares two values using a shared denominator.
- Equal nonzero values have a 0% difference; the result is never negative.
- When one value is zero and the other is not, this method gives 200%.
- Two zeros produce an undefined result because the denominator is zero.
How to use the percentage difference calculator
Enter Value A and Value B in the same units, then select Calculate. Decimals and negative values are accepted. Compare like quantities: two dollar amounts or two lengths measured in the same unit, for example.
This method is useful for comparing two positive price quotes, measurements or estimates without choosing one as the baseline. It does not tell you whether either value is accurate, whether a difference is statistically significant or what caused it.
Percentage difference formula
Percentage difference = |A − B| ÷ [(|A| + |B|) ÷ 2] × 100
The bars mean absolute value: use the distance from zero. For two positive inputs, the denominator is simply their ordinary average. For negative inputs, this calculator uses the average of their magnitudes.
For 75 and 100:
- The absolute difference is 25.
- Their average is 87.5.
- 25 ÷ 87.5 × 100 = 28.57%.
| Value A | Value B | Percentage difference |
|---|---|---|
| 75 | 100 | 28.57% |
| 80 | 100 | 22.22% |
| 82 | 88 | 7.06% |
| 100 | 100 | 0.00% |
| 0 | 50 | 200.00% |
| −10 | −20 | 66.67% |
| −10 | 10 | 200.00% |
| 0 | 0 | Undefined |
With opposite signs, the absolute gap equals the sum of the magnitudes, so this method returns 200%. That result can be mathematically consistent yet unhelpful for describing a business moving from a loss to a profit. Report the actual values and the absolute change in that situation.
Percentage difference vs. percentage change
Percentage change uses the original value as its denominator and describes direction. Percentage difference uses the average magnitude of the pair and does not assign a starting point.
From 80 to 100, the percentage increase is 25%. Comparing 80 and 100 without a baseline gives a percentage difference of 22.22%. Both answers can be correct because they answer different questions.
For two percentages, also consider percentage points. Moving from 4% to 5% is a rise of 1 percentage point, a 25% relative increase, or a 22.22% symmetric percentage difference. The Office for National Statistics explains percentage points as the difference between percentages.
Frequently asked questions
Can percentage difference be negative?
Not with this calculator’s formula. It uses an absolute gap and a positive denominator whenever at least one input is nonzero. Equal nonzero inputs return zero.
Is percentage difference the same as percent error?
No. Percent error compares a measured value with an accepted reference value. Percentage difference treats the two inputs symmetrically. Choose the method that fits the question you are answering.
Can I use this for relative percent difference in a laboratory report?
Follow the method required by the laboratory or protocol. Relative-difference conventions can use different denominators; NIST documents several percentage-difference methods. This calculator’s average-magnitude convention should not replace a specified method.
Why does zero compared with zero show undefined?
Both values are equal, but the percentage formula also needs a nonzero denominator. Their average magnitude is zero, so there is no percentage result under this method.
For calculations with a clear before-and-after order, use percentage change. Find other tools in the financial calculator library.
*National Savings Rate Average as published by FDIC