Percentage change calculator
Work out the percentage increase or decrease between two values. The calculator shows the relative change as a percentage and the absolute difference, so the two never get confused.
Going from 80 to 100 is a +25% change.
Formula
P is the starting value and K the ending value. You always divide by the starting value, because that is the reference point.
How we got there
A positive answer is an increase, a negative one a decrease. A decrease never passes −100%, since you cannot take away more than the whole.
How to work out a percentage change by hand
- Subtract the starting value from the ending value
100 − 80 = 20. That is the absolute difference — how much the value moved.
- Divide the difference by the starting value
20 ÷ 80 = 0.25. The reference point is always where you started, not where you ended.
- Multiply by 100
0.25 × 100 = 25%, an increase of 25%.
- Remember that increases and decreases are not symmetric
Going 80 → 100 is +25%, but 100 → 80 is −20%. The denominator differs, so the percentage differs too.
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Frequently asked questions
Subtract the starting value from the ending value, divide by the starting value and multiply by 100. From 80 to 100 gives +25%.
Because each percentage is taken from a different base. 80 plus 25% is 100, but 100 minus 25% is 75.
The plain difference between the two values, with no division. The calculator shows it next to the percentage.
A percentage change cannot be calculated — dividing by zero has no answer. The calculator returns a dash.
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