Percentage Difference Calculator

Compare two values: get the absolute difference, the symmetric percentage difference |A − B| ÷ average × 100, and the percentage change from the baseline you choose, with formulas and clear handling of zeros.

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About the Percentage Difference Calculator

Percentage Difference Calculator compares two numbers side by side. It shows the absolute difference, the percentage difference — which compares the gap with the average of the two values and gives the same answer whichever order you enter them — and the percentage change from whichever value you choose as the starting point.

The two measures answer different questions: percentage difference is for comparing two values that have no natural “before” and “after”, such as two measurements or two prices, while percentage change describes growth or decline from a baseline. Both formulas are shown with your numbers. Decimals and negative values are handled consistently, and the calculator explains when a result is undefined, for example when both values are zero or the baseline is zero.

How to use

Enter Value A and Value B.
Choose which value is the baseline for the percentage change.
Click Compare.
Read the absolute difference, percentage difference and percentage change with their formulas.
Copy or download the summary.

Key features

Absolute difference |A − B|.
Percentage difference: |A − B| ÷ ((|A| + |B|) ÷ 2) × 100.
Percentage change from a selectable baseline.
Consistent handling of decimals and negative numbers.
Clear explanations when a result is undefined.
Formulas with your values, Copy Summary, Download Summary, Reset and Back.

Best practices

Use percentage difference when neither value is a natural starting point.
Use percentage change when you are measuring growth or decline over time.
Pick the baseline carefully — the change from A to B is not the same as from B to A.
Be cautious interpreting percentages when values have different signs.
Report which formula you used so others can interpret the number correctly.

Benefits

Avoids the common mix-up between difference and change.
Both measures side by side for the same pair of values.
Transparent formulas you can verify.
Private: calculations run in your browser.

Frequently asked questions

What is the formula for percentage difference?

Percentage difference = |A − B| ÷ ((|A| + |B|) ÷ 2) × 100. It divides the gap by the average size of the two values, so swapping A and B gives the same result.

How is that different from percentage change?

Percentage change = (new − baseline) ÷ |baseline| × 100. It depends on which value is the starting point: going from 100 to 150 is +50%, but going from 150 to 100 is −33.33%. The percentage difference between 100 and 150 is 40% either way.

Why is the result undefined when both values are zero?

The average of the two values is zero, and dividing by zero is not possible. Similarly, percentage change is undefined when the baseline is zero.

How are negative numbers handled?

Percentage difference uses absolute values in the average. Percentage change divides by the absolute value of the baseline, so a move from −50 to −25 is reported as an increase of 50%.

Can percentage difference be more than 100%?

Yes. It can reach up to 200% for values of the same sign that are far apart, or when the values have opposite signs.

How is this different from the Percentage Change tool?

Toolsfy’s Percentage Change tool focuses on change from an old to a new value and applying a percentage. This calculator compares two values and shows the symmetric percentage difference alongside the change.