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Percent Change — Definition, Formula & Examples

Percent change is the amount a value has increased or decreased, expressed as a percentage of the original value. It tells you how big a change is relative to where you started.

Percent change is the ratio of the difference between a new value and an original value to the original value, multiplied by 100. A positive result indicates a percent increase; a negative result indicates a percent decrease.

Key Formula

Percent Change=New Value−Original ValueOriginal Value×100\text{Percent Change} = \frac{\text{New Value} - \text{Original Value}}{\text{Original Value}} \times 100
Where:
  • New Value\text{New Value} = The value after the change
  • Original Value\text{Original Value} = The starting value before the change

How It Works

Start by subtracting the original value from the new value. Divide that difference by the original value. Multiply the result by 100 to convert it to a percentage. If your answer is positive, the value increased; if negative, it decreased.

Worked Example

Problem: A jacket originally costs $80. It is now on sale for $60. What is the percent change in price?
Find the difference: Subtract the original value from the new value.
60−80=−2060 - 80 = -20
Divide by the original: Divide the difference by the original price.
−2080=−0.25\frac{-20}{80} = -0.25
Convert to a percentage: Multiply by 100.
−0.25×100=−25%-0.25 \times 100 = -25\%
Answer: The price decreased by 25%.

Why It Matters

Percent change appears constantly in everyday life — comparing sale prices, tracking population growth, and reading news about economic data. In science classes, you use it to calculate percent error between measured and expected results. It is also foundational for high school topics like exponential growth and finance.

Common Mistakes

Mistake: Dividing by the new value instead of the original value.
Correction: Always divide by the original (starting) value. The original is your reference point for how big the change is.