● Percent Difference Calculator ●

Enter any two numbers. Order does not matter — swapping A and B gives the exact same answer (that is the whole point of percent difference).

Value A

Value B

Percent difference

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Absolute difference |A−B|

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Average (A+B)/2

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Ratio A : B

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Show your work

⚖️ Percent Difference vs Percent Change — which one do you need?

These two sound alike but answer different questions. Picking the wrong one is the #1 mistake people make with these calculators.

📐 Percent Difference ← this tool

Symmetric. Answers: "How far apart are these two numbers?"

|A−B| ÷ ((A+B)/2) × 100

No direction: A↔B gives the same answer
Always ≥ 0% — can never be negative
Use when neither value is "the original"

📈 Percent Change (sibling tool)

Directional. Answers: "How much did it go up/down from old to new?"

(new−old) ÷ |old| × 100

Direction matters: old→new ≠ new→old
Can be negative (a decrease)
Use for growth, discounts, before/after

Concrete example — 10 vs 14: percent difference = 33.33% (symmetric), while percent change from 10 → 14 = 40%. Different questions, different answers. For directional change, see our percent change calculator.

When to use percent difference (decision table)

Rule of thumb: if you can point at one value and say "this is the starting point", use percent change. If the two values just sit side by side, use percent difference.

Your situation	Use this
Comparing two test scores, two prices, two measurements — no "before/after"	Percent difference
Experimental result vs theoretical / accepted value (physics & chemistry lab work)	Percent difference
Two candidate products, schools, or cities compared side by side	Percent difference
Quality-control: two samples from the same batch	Percent difference (a.k.a. relative percent difference)
Price then vs now, salary raise, weight loss, stock movement	Percent change
Growth year-over-year, discount off original price	Percent change
Measured value vs a known true value (error analysis)	Percent error

● Multi-Pair Mode ●

Compare several pairs at once — one pair per line. Separators: comma, space, semicolon, or "vs". Example: 80, 90
Note: percent difference is defined per pair — for three or more numbers, list them pairwise (A vs B, B vs C, …).

Worked examples (step by step)

📝 Example 1 — Test scores: 80 vs 90

Absolute difference: |80 − 90| = 10

Average: (80 + 90) ÷ 2 = 85

Divide & ×100: 10 ÷ 85 × 100 = 11.7647…%

Answer: 11.76% difference

🛒 Example 2 — Prices: $24.99 vs $19.99

Absolute difference: |24.99 − 19.99| = 5.00

Average: (24.99 + 19.99) ÷ 2 = 22.49

Divide & ×100: 5.00 ÷ 22.49 × 100 = 22.2321…%

Answer: 22.23% difference

🔬 Example 3 — Physics lab: theoretical 9.81 vs measured 9.65

Absolute difference: |9.81 − 9.65| = 0.16

Average: (9.81 + 9.65) ÷ 2 = 9.73

Divide & ×100: 0.16 ÷ 9.73 × 100 = 1.6443…%

Answer: 1.64% difference

Methodology — how this calculator works

Formula (canonical): percent difference = |A − B| / ((A + B) / 2) × 100. The denominator is the average of the two values — that is what makes the result symmetric: swapping A and B never changes the answer.
Why the average? Dividing by the average treats neither value as privileged. (Dividing by A or by B would give two different answers — that is percent change, not difference.)
Always non-negative: the absolute value in the numerator — and on the final quotient — guarantees the result is ≥ 0%. Percent difference can never be negative.
Can exceed 100%: when one value is much larger than the other (e.g. 0 vs 10 → 200%). There is no upper bound.
Undefined case (honest): when the average of the two values is zero — e.g. 5 vs −5, or 0 vs 0 — the division has no meaning, so this calculator says so instead of inventing a number.
Negative inputs: both-negative pairs (e.g. −10 vs −14) are handled by taking the magnitude of the quotient, since percent difference is unsigned by convention. Mixed-sign pairs are computed with the signed average.
Precision: results are computed in double-precision floating point and displayed rounded to 4 decimal places (trailing zeros trimmed).
Privacy: every calculation runs locally in your browser. This page makes zero network requests — your numbers never leave your device.

🔒 Privacy: all calculations run locally in your browser. No data is sent anywhere — there is nothing to send to; the page makes zero network requests.

Percent Difference in Excel & Google Sheets

Put the two numbers in A1 and B1, then use:

=ABS(A1-B1)/AVERAGE(A1,B1)*100

Format the cell as Percentage (or divide by 100 first: =ABS(A1-B1)/AVERAGE(A1,B1) with % formatting). Watch out: if A1 = −B1 the average is zero and Excel returns #DIV/0! — the same honest "undefined" this calculator reports.

Percent Difference Calculator