Relative change — quick, practical guide
Core idea
Relative change tells you how much a value moved versus where it started. It’s the proportional change, typically shown as a percentage, so changes are comparable across different scales.
How it works
Formula: (New − Old) / Old × 100%
- Old: reference/baseline value (must not be 0)
- New: the updated/current value
- Sign: + means increase, − means decrease
Sanity checks
- If New = Old → 0%
- If New = 0 and Old > 0 → −100%
- If New = 2 × Old → +100%
Shortcuts
- Growth factor = New / Old. Relative change = (factor − 1) × 100%
- For small moves, log changes ≈ percent change
Pitfalls
- Old = 0 makes the percent undefined
- Percent up then down isn’t symmetric (e.g., +25% then −25% ≠ 0%)
- Small Old values exaggerate percentages
Micro‑examples
- Old 100 → New 120: (120−100)/100 = 20%
- Old 80 → New 60: (60−80)/80 = −25%
- Old 50 → New 75: factor 1.5 → +50%
Mini‑FAQ
Relative vs absolute change? Absolute is New−Old. Relative scales that by Old to compare across sizes.
What if values are negative? The formula still works, but interpretation depends on context; consider using absolute or a different baseline.
Action tip
When comparing multiple items, normalize using the same baseline period and show both absolute and relative change for clarity.