Percentage Change Calculator

Q: How do I calculate percentage change?

Subtract the old value from the new, divide by the old value, and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% increase.

Q: Why isn't a 25% increase reversed by a 25% decrease?

Because the base changes. 80 up 25% is 100, but 100 down 25% is 75, not 80 — the decrease is taken from the larger number. This asymmetry catches people out with investment gains and losses.

Q: What is percentage difference?

Percentage difference compares two values without a clear 'before,' dividing the absolute difference by their average. It differs from percentage change, which measures movement from a specific starting value.

Find the percentage increase or decrease between any two numbers, plus the raw difference.

Percentage change

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Direction

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Absolute difference

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Ratio (new ÷ old)

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The formula

% change = ((New − Old) ÷ |Old|) × 100

Worked example

80 → 100: (100 − 80) ÷ 80 × 100 = +25% (increase). Reverse, 100 → 80: (80 − 100) ÷ 100 × 100 = −20%.

The asymmetry that trips people up

A 25% gain and a 25% loss don't cancel out, because each percentage is taken from a different base. This matters most with money: a stock that drops 50% must then rise 100% just to break even, not 50%. That's why average returns can mislead and why CAGR exists. For directionless comparisons (like the difference between two measurements with no clear "before"), percentage difference — dividing by the average — is the right tool instead. For money-specific change, see the discount and ROI calculators.

Frequently asked questions

How do I calculate percentage change?

(New − Old) ÷ Old × 100. 80 → 100 = +25%.

Why isn't a 25% increase reversed by a 25% decrease?

The base changes — 80 up 25% is 100, but 100 down 25% is 75.

What is percentage difference?

Absolute difference ÷ the average of the two values — for comparisons with no clear starting point.

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Last reviewed: July 2026.