Skip to content
calculatorpro

Percentage Difference Calculator

For comparing two numbers where neither one is the “before”. The gap is measured against the midpoint of the two, so the answer stays the same whichever order you type them in — which is exactly what makes this a different sum from percentage change.

  • Free
  • No account needed
  • Nothing leaves your browser

Neither number is the "before" here…

…so swapping the two would not change the answer.

Loaded with an example. Type over either field.

Answer

18.18%

The difference between 150 and 180 is 18.18%

First number
150
Second number
180
The gap
30

What each figure is

A percentage means nothing on its own. These are the numbers it is made of.

  • First numberYou entered thisneither number is the "before" here150
  • Second numberYou entered thisswapping the two would not change the answer180
  • The gapthe distance between them, ignoring direction30
  • The midpointwhat the gap is measured against165

How that was worked out

Each step, and why it is that step.

  1. Step 1 — Find the gap

    |150 − 180| = 30

    Difference has no direction, so the sign is dropped here rather than carried through.

  2. Step 2 — Find the midpoint

    (150 + 180) ÷ 2 = 165

    With no starting figure to measure against, the fair reference is halfway between the two.

  3. Step 3 — Divide, then scale to a hundred

    30 ÷ 165 × 100 = 18.18%

    Same last step as every other percentage question.

The mistake this prevents

As a CHANGE from 150 to 180 this is 20%, measured against 150 rather than the midpoint. Use change when one number came first; use difference when neither did.

Check this before you rely on it. A free everyday calculator, provided as a guide — not tax, accounting, financial or legal advice. The working is shown above so you can verify it against your own figures. See our terms of use.

How it works

STEP 1

Enter both numbers

In either order. Two measurements of the same thing, two quotes for the same job, two departments’ figures — anything where calling one of them "first" would be arbitrary.

STEP 2

The gap is measured against the midpoint

With no starting figure to divide by, the fair reference is halfway between the two. That is what keeps the answer symmetric, and the midpoint is shown as its own line so you can see what it used.

STEP 3

Check it is the sum you wanted

The page also shows what the same pair reads as a percentage change. If one of your numbers really did come first, that is the figure you want, and there is a calculator for it.

The guideHow to calculate percentages — the five sums people actually needTo find P% of a number, multiply by P ÷ 100. To find what one number is as a percentage of another, divide the part by the whole and multiply by 100.Read it

Common questions

What is the percentage difference formula?

|a − b| ÷ ((a + b) ÷ 2) × 100. For 150 and 180: the gap is 30, the midpoint is 165, and 30 ÷ 165 × 100 = 18.18%. The absolute-value bars matter — a difference has no direction.

How is this different from percentage change?

Change divides by the figure that came first and carries a sign: 150 to 180 is +20%, and 180 to 150 is −16.67%. Difference divides by the midpoint and is symmetric: both pairs give 18.18%. Swap your two numbers — if the answer ought to stay put, you want difference.

Which one should I use?

Use change when there is a before and an after — last year against this year, the old price against the new. Use difference when the two numbers simply exist side by side, like two lab measurements or two suppliers’ quotes. Using change there would make the answer depend on which one you happened to write down first.

Why divide by the average rather than by one of the numbers?

Because picking either one would privilege it, and the answer would change if you swapped them. The midpoint treats both equally, which is the whole point of the measure. It is the convention in scientific and engineering comparisons for the same reason.

What if the two numbers average zero?

There is no answer — the sum would divide by zero. That happens with pairs like −50 and 50, and the calculator says so rather than printing something misleading.

Related calculators

Percentage Calculator

Percentage of a number, increase, decrease and difference.

Ratio Calculator

Simplify a ratio, scale it up, or find the missing part.

Margin & Markup Calculator

Turn cost into price, or price into margin — without the platform fees.