Percentage Change: Increase and Decrease
How to calculate percentage increase and decrease with the percentage change formula, worked examples and the mistake to avoid.
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Frequently asked questions
How do I calculate percentage change?
Subtract the old value from the new, divide by the old value, and multiply by 100: (new − old) ÷ old × 100.
What is the difference between percent increase and decrease?
An increase is a positive percentage change (new is larger); a decrease is negative (new is smaller). The formula is the same.
Why isn’t a 20% rise cancelled by a 20% fall?
Because each percentage is based on a different starting value. The fall is calculated from the higher number, so it removes more.
Which number goes on the bottom of the formula?
The original (old) value always goes in the denominator, since change is measured relative to the starting point.
How do I find the new value after a percentage change?
Multiply the old value by (1 + change ÷ 100). A 25% rise on 80 is 80 × 1.25 = 100.
Can percentage change be more than 100%?
Yes. If a value more than doubles, the increase exceeds 100% — going from 50 to 150 is a 200% increase.
Calculating percentage change
Percentage change measures how much a value has grown or shrunk relative to its starting point. The formula is (new − old) ÷ old × 100. A positive result is an increase; a negative result is a decrease.
Worked examples
If a value rises from 80 to 100: (100 − 80) ÷ 80 × 100 = 25% increase. If it falls from 100 to 80: (80 − 100) ÷ 100 × 100 = −20%, a 20% decrease. Note the two percentages differ because the starting value (the denominator) is different.
Why increases and decreases are not symmetric
A 25% rise followed by a 25% fall does not return you to the start. 80 up 25% is 100, but 100 down 25% is 75. Each percentage is taken from a different base, which is a common source of confusion in reporting.
Always be clear about which value is "old" and which is "new". Percentage change is widely used for prices, populations, investment returns and any figure tracked over time.
Results are estimates for general guidance in Netherlands and may not reflect the latest local rates, fees or rules. Check official sources before making decisions.