Everyday Math
Percentage Difference Calculator
Use percentage difference when neither number is the 'before' — two quotes, two stores, two measurements, two test results. It compares the gap to the average of both values, so the answer is the same whichever you enter first. The calculator also shows the directional percent change both ways so you can see why the numbers differ.
Estimates only. Verify important figures against your own records before acting on them. See our disclaimer.
How to use the Percentage Difference Calculator
- Enter the value a and value b.
- Read the highlighted result first, then the breakdown below it. Load the worked example to check the math by hand.
What this calculator includes
What you enter
- Value A
- Value B
What you get back
- Percentage difference
- Absolute difference
- Average of the two values
- Percent change A → B
- Percent change B → A
How this calculation works
Percentage difference has no direction. It divides the absolute gap by the average of the two values, which is why swapping A and B gives the same result. Percent change, by contrast, picks one value as the base and so gives two different answers.
- Absolute difference = |A − B|
- Average = (|A| + |B|) ÷ 2
- Percentage difference = absolute difference ÷ average × 100
What the result means
Percentage difference is the size of the gap relative to the midpoint of the two values. It has no direction, so it answers 'how far apart are these?' rather than 'how much did this change?'.
Common mistakes and assumptions
- Using percentage difference for a before/after change — use percent change instead.
- Comparing values with opposite signs, where the average can be misleading.
- Quoting it next to percent change figures without saying which one you used.
Worked example
Two contractors quote $120 and $150 for the same job.
- 1Absolute difference = |120 − 150| = 30.
- 2Average = (120 + 150) ÷ 2 = 135.
- 3Percentage difference = 30 ÷ 135 × 100 ≈ 22.22%.
- 4By contrast, 120 → 150 is a 25% increase and 150 → 120 is a 20% decrease.
Frequently asked questions
- When should I use percentage difference instead of percent change?
- Use percentage difference when two values are peers and neither is the starting point — two prices, two measurements, two samples. Use percent change when there is a clear before and after.
- Why is the percentage difference between 120 and 150 not 25%?
- 25% is the percent change from 120 up to 150, which uses 120 as the base. Percentage difference uses the average (135) as the base, giving about 22.2%.
- Can percentage difference be more than 100%?
- Yes, up to a maximum of 200% when one value is zero and the other is not. That ceiling is one reason it is used for comparisons that include zero.
- Does the order of the values matter?
- No. |A − B| and the average are the same either way, so the result is symmetric.
Disclaimer
This calculator returns estimates based only on the values you enter. It does not account for taxes, financing terms, local regulations, or conditions specific to your operation, and it is not accounting, legal, tax, or investment advice. Confirm any figure that carries real cost before you rely on it.
Calculations run entirely in your browser and the numbers you type are never sent to us or stored. Read how Answerivo calculators are built or report a correction. About Answerivo.