Guide
How to Calculate Percentage Change (Increase and Decrease)
Learn the percentage-change formula, the difference between absolute and relative change, and common pitfalls.
Percentage change measures how much a value has grown or shrunk relative to its starting point. It is the standard way to report growth in business, science, and everyday life.
The percentage-change formula
Percentage change = ((New − Old) ÷ |Old|) × 100
A positive result is an increase; a negative result is a decrease. Using the absolute value of the old number in the denominator keeps the sign meaningful.
Absolute vs. relative change
Absolute change is the simple difference (New − Old). Relative change (the percentage) expresses that difference as a proportion of the original. A $10 rise on a $50 item is a 20% increase; the same $10 rise on a $500 item is only a 2% increase. The percentage tells you the scale of the change.
How to use the calculator
- Enter the original (old) value.
- Enter the new value.
- Read the percentage change and the absolute difference.
Examples
Sales rising from 1,200 to 1,500 units: ((1,500 − 1,200) ÷ 1,200) × 100 = 25% increase. A stock falling from $80 to $60: ((60 − 80) ÷ 80) × 100 = −25%, a 25% decrease.
When percentage change is useful
- Reporting revenue, traffic, or user growth.
- Comparing prices or costs over time.
- Analysing experiment results in science.
- Understanding news headlines about economic change.
Common mistakes
Percentage changes are not symmetric: a 50% increase followed by a 50% decrease does not return you to the start. $100 → +50% → $150 → −50% → $75. Always calculate from the correct base.
Put it into practice
Use the Percentage Change Calculator right now — free, in your browser, no sign-up required.
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