Percentage Difference Calculator
Calculate the percentage difference between two values. Unlike percent change, this is order-independent and uses the average as the base
Percentage Difference vs Percentage Change
Percentage difference is for comparing two values without a reference 'starting' value: |a - b| / ((a + b) / 2) × 100. So comparing 10 vs 20: |10-20| / 15 = 66.7% difference. Symmetric - same answer regardless of which value comes first. Used when neither value is the 'original' or 'new'.
Percentage change uses one as a baseline: (New - Original) / Original × 100. Going from 10 to 20: 100% change (doubled). Going from 20 to 10: -50% change (halved). NOT symmetric. Use percentage change for time-series comparisons (this year vs last); use percentage difference for parallel comparisons (London prices vs Paris prices).
Percentage Difference Examples
| Value A | Value B | % Difference |
|---|---|---|
| 10 | 12 | 18.2% |
| 10 | 20 | 66.7% |
| 50 | 55 | 9.5% |
| 100 | 120 | 18.2% |
| 100 | 200 | 66.7% |
| 50 | 100 | 66.7% |
| £10 | £12.50 | 22.2% |
| 72 kg | 75 kg | 4.1% |
Frequently Asked Questions
When should I use difference vs change?
Use difference for symmetric comparisons (Comparing two products' prices when neither is the 'original'). Use change for time-series (this year's revenue vs last year's). Use change when there's a clear 'before' and 'after'.
Why does percentage difference feel different from percentage change?
Difference uses the average of both values as denominator (giving symmetric, smaller numbers). Change uses one specific value (giving asymmetric results that depend on direction). 100 vs 200: change is 100% (one direction) or 50% (other). Difference is always 66.7%.
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