Percentage change shows how much a value has increased or decreased compared with its original value. It is useful for prices, sales, traffic, weight, costs, test scores, revenue, and many other before-and-after comparisons. The key is to compare the change with the original value, not just the new value.
Use the calculator to check the number quickly, then read the guide for formulas, examples, and common mistakes.
What Is Percentage Change?
Percentage change measures how much a number changes compared with where it started.
If a value rises from 100 to 120, the change is 20. Compared with the original value of 100, that is a 20% increase.
If a value falls from 100 to 80, the change is 20. Compared with the original value of 100, that is a 20% decrease.
Percentage Change Formula
The percentage change formula is: percentage change = (new value - old value) ÷ old value × 100.
The old value is the starting number. The new value is the number after the change.
If the answer is positive, the value increased. If the answer is negative, the value decreased.
Step 1: Find the Old Value
The old value is the original number before the change happened.
This is the base of the calculation. Using the wrong base can make the percentage change wrong.
For example, if a price changed from 80 to 100, the old value is 80.
Step 2: Find the New Value
The new value is the number after the change happened.
In the same example, the new value is 100.
The calculation compares this new value with the original value.
Step 3: Find the Difference
Subtract the old value from the new value.
If the price changed from 80 to 100, the difference is 100 - 80, which equals 20.
This difference is the amount of change.
Step 4: Divide by the Old Value
After finding the difference, divide it by the old value.
Using the same example, 20 ÷ 80 = 0.25.
This shows the change as a decimal compared with the starting value.
Step 5: Multiply by 100
Multiply the decimal by 100 to convert it into a percentage.
0.25 × 100 = 25%.
So the value increased by 25%.
Percentage Increase Example
Suppose website visits increase from 2,000 to 2,500.
The change is 2,500 - 2,000, which equals 500.
Percentage change is 500 ÷ 2,000 × 100, which equals 25%. For more examples, read Percentage Increase Formula.
Percentage Decrease Example
Suppose a cost decreases from 300 to 240.
The change is 240 - 300, which equals -60.
Percentage change is -60 ÷ 300 × 100, which equals -20%. This means the value decreased by 20%. For more examples, read Percentage Decrease Formula.
Why the Original Value Matters
The original value matters because percentage change is measured from the starting point.
An increase from 50 to 100 is a 100% increase. A decrease from 100 to 50 is a 50% decrease.
The movement looks similar in numbers, but the percentage changes differ because the starting value is different.
Common Percentage Change Mistakes
The first mistake is dividing by the new value instead of the old value.
The second mistake is ignoring whether the result is positive or negative.
The third mistake is assuming that a percentage increase and the same percentage decrease cancel each other out. A 20% increase followed by a 20% decrease does not usually return to the original value.
Use the Calculator
Use the Percentage Calculator when you need a quick percentage calculation.
For the general formula, read How to Calculate Percentage.
For simple percentage-of-a-number calculations, read How to Calculate Percentage of a Number.
Conclusion
Percentage change compares the difference between two values with the original value.
Use new value minus old value, divide by the old value, and multiply by 100. A positive result means increase, while a negative result means decrease.
Related guides and tools
FAQs
What is the percentage change formula?
Percentage change = (new value - old value) divided by old value, multiplied by 100.
What does a positive percentage change mean?
A positive result means the value increased.
What does a negative percentage change mean?
A negative result means the value decreased.
Should I divide by old value or new value?
Use the old value because percentage change is measured from the starting number.