How to Calculate Percentage Increase and Decrease
Learn the percentage change formula with everyday examples involving prices, measurements and business figures.
In this guide
The basic idea
Percentage change tells you how large a change is compared with where you started. The starting value matters. That is why a move from 100 to 120 is a 20% increase, while a move from 120 back to 100 is a 16.67% decrease. The two percentages are not mirror images.
The formula
Take the new value minus the original value, divide the result by the original value, then multiply by 100. A positive result represents an increase and a negative result represents a decrease.
A price increase example
Suppose a service rises from 500 to 575. The change is 75. Divide 75 by 500 and multiply by 100: the increase is 15%. This is often the quickest way to check a price adjustment.
A decrease example
If stock falls from 800 units to 680, the difference is -120. Compared with the original 800, that is a 15% decrease. Always compare the change with the starting figure when reporting percentage change.
A common mistake
Using the new value as the denominator changes the question. It can be useful for some other calculations, but it is not the standard percentage-change calculation. If the wording says “increase from A to B”, A is normally the reference point.
Try the related tool
If you came here because you need to do the calculation or create something now, you can use the matching KingToolsKit tool and then come back to the guide when you want the explanation.
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