What is the percentage difference formula?

Percentage difference equals the absolute value of Value 1 minus Value 2, divided by the average of the two values, multiplied by 100.

Why does the formula divide by the average instead of one of the values?

Percentage difference treats both values as equals — neither is a "before" or "after" — so it divides by their shared average instead of picking one value as the base.

Does the order of the two values matter?

No. Because the numerator uses an absolute value and the denominator is the average of both values, swapping Value 1 and Value 2 always gives the exact same result.

Can percentage difference be negative?

No. The absolute value in the numerator means percentage difference is always zero or positive — it measures how far apart two values are, not which one is bigger.

What's the difference between percentage difference and percentage change?

Percentage change assumes an order — a starting value and an ending value — and its sign shows increase or decrease. Percentage difference compares two values with no order and is always positive relative to their average.

When should I use percentage difference instead of percentage change?

Use percentage difference when comparing two values that are equally valid — like two lab measurements or two competitors' prices — where neither one is naturally the "original."

Percentage Difference Calculator

What is percentage difference?

Percentage difference compares two values that have no natural order — neither one is a starting point or an ending point, they're just two numbers being measured against each other.

$\text{Percentage difference} = \frac{|V_1 - V_2|}{\dfrac{V_1 + V_2}{2}} \times 100$

Tip: Order doesn't matter here. Swap Value 1 and Value 2 and you get the exact same percentage — that's the whole point of using "difference" instead of "change."

Why the formula divides by the average

Unlike percentage change, which measures against a single starting value, percentage difference divides by the average of both values, (V₁ + V₂) / 2. That average sits exactly between the two numbers, so it doesn't favor either one as the "correct" base.

Example — comparing 5 and 7.

$\frac{|5 - 7|}{\frac{5+7}{2}} \times 100 = \frac{2}{6} \times 100 \approx 33.33\%$

Reverse the values — 7 and 5 — and the average is still 6, the absolute difference is still 2, and the result is still 33.33%.

Why order never matters

Two things make percentage difference symmetric: the numerator takes an absolute value, and the denominator is an average of both inputs rather than either one alone. Both of those are unaffected by which value you call "first."

Example — 40 and 60.

$\frac{|40 - 60|}{\frac{40+60}{2}} \times 100 = \frac{20}{50} \times 100 = 40\%$

Compare that to treating 40 as a starting value and 60 as an ending value: percentage change would give 50%, because it divides by 40 alone instead of the average of 50. The two formulas answer different questions.

Worked examples

Two values close together — 98 and 102.

$\frac{|98-102|}{\frac{98+102}{2}} \times 100 = \frac{4}{100} \times 100 = 4\%$

A small absolute gap between two similar numbers gives a small percentage difference.

Identical values — 100 and 100.

$\frac{|100-100|}{\frac{100+100}{2}} \times 100 = \frac{0}{100} \times 100 = 0\%$

Two equal values always have a 0% difference.

Percentage difference vs. percentage change

Tip: Use percentage change when you have a clear "before" and "after." Use percentage difference when comparing two values with no natural order — the result is always positive and relative to their average.

Percentage difference only makes sense for values that are meaningfully comparable on the same scale — it's typically applied to positive numbers, like two measurements, two prices, or two survey results.

Common mistakes

Dividing by one value instead of the average. That's the percentage change formula, not percentage difference — it gives a different (and order-dependent) answer.
Forgetting the absolute value. Without it, percentage difference could come out negative, which contradicts the idea that it's a symmetric, order-independent measure.
Applying it when there's a clear before/after. If one value really is the original and the other is the result, percentage change is the more meaningful formula.

Where percentage difference shows up

Science — comparing two experimental measurements of the same quantity.
Business — comparing prices, ratings, or metrics between two competitors.
Everyday comparisons — comparing two estimates or quotes where neither is the "correct" baseline.