Percentage Change Calculator
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Percent change from an old value to a new value — positive for increases, negative for decreases.
Old & new value
Percentage change
+20%
Absolute change: +20
- Increase
- 20
Related calculators
Percentage change
Percentage change measures how much a value has grown or shrunk relative to its starting point: percent change = (new value − old value) ÷ old value × 100. A positive result is an increase; a negative result is a decrease.
Percentage change is always relative to the old (starting) value, not the new one — that's why a 50% increase followed by a 50% decrease does not return you to the original number. Going from 100 to 150 is a 50% increase, but going back from 150 to 100 is only a 33.3% decrease.
Example: a price that rises from 100 to 120 has increased by 20 (the absolute change) and by 20% ((120 − 100) ÷ 100 × 100). A drop from 120 back to 100 would be a decrease of about 16.7%, not 20%.
Common questions
Why isn't a 20% increase undone by a 20% decrease?
Because each percentage is calculated from a different base value. Increasing 100 by 20% gives 120, but decreasing 120 by 20% gives 96, not 100 — the base value changed.
What does a negative percentage change mean?
A negative result means the new value is smaller than the old value — in other words, a percentage decrease rather than an increase.