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Percentage Difference Calculator

Compare two nonnegative measurements using their average as a symmetric percentage base.

Your numbers

Make it your own
Updates as you type
Symmetric percentage difference
22.2222%

Calculated from your inputs · rounded for display

Absolute difference20
Average base90

For two nonnegative measurements. This is not percentage change from an original value.

Your calculation, step by step

No black boxes
  1. |80 − 100| ÷ ((80 + 100)/2) × 100.

How to use this calculator

  1. Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
  2. Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
  3. Copy, share, save, or download your result. Saved inputs stay on this device.

How the calculation works

Difference (%) = |a−b| / [(a+b)/2] × 100

Unlike percentage change, this comparison treats neither measurement as the original baseline. Inputs must be nonnegative and cannot both be zero because their average would give a zero denominator. Review the units, period and assumptions before comparing scenarios. Displayed values are rounded, while the underlying calculation retains its available precision.

A worked example

For 80 and 100, the average is 90 and absolute difference is 20, so percentage difference is 22.2222%.

Reading your result

Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.

Frequently asked questions

What assumptions does this calculation use?

Unlike percentage change, this comparison treats neither measurement as the original baseline. Inputs must be nonnegative and cannot both be zero because their average would give a zero denominator.

Can I save or check a scenario?

The result includes the working and supporting values. Save and Restore keep inputs on this device; Copy, Download and Print export the result. Sharing a scenario explicitly includes the inputs in its link.

Sources & methodology

This calculator uses the mathematical identity and assumptions stated above. No current rates, prices, or external data are loaded. Conversion tools use international unit definitions.

Formula review: October 24, 2026. Read our methodology.