Quick answer: Percentage decrease shows how much a value falls compared with where it started. The method is the same as percentage increase, but the change is negative.
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Understand the method
Compute (new − original) ÷ original × 100. With positive original values, a negative result indicates a decrease. If you want the size of the drop, express its magnitude as a positive percentage and label it clearly.
Be careful when comparing negative starting values: interpreting the sign of percentage change becomes less intuitive. Explain the situation in words and use an absolute-difference measure where appropriate.
Worked example
A cost drops from $250 to $200. The change is −$50. Dividing by $250 gives −0.20, or a 20% decrease.
What people often get wrong
Dividing by the new value instead of the original would incorrectly label this 25%.
A practical way to use this
Use the same time period or measurement basis on both sides of the comparison.
Frequently asked question
Can a value fall by 100%? With a positive starting value, falling to zero is a 100% decrease.
A decrease uses the same calculation
A price moving from $250 to $200 changes by −$50. Divide by the original $250 and multiply by 100 to get −20%. It can be described as a 20% decrease. Use the original figure for comparisons, not the final price.
Apply it to your own task
A common mistake is taking the difference and dividing by the smaller figure. That computes a different percentage and can overstate the size of a decrease.
Related reading
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