Percentage Change Calculator
Enter an original value and a new value to find the percentage increase or decrease.
What Is Percentage Change?
Percentage change tells you how much something has increased or decreased relative to its starting point. It is one of the most useful ideas in finance, business, school math, and everyday life. You can use it to compare prices, test scores, website traffic, savings growth, or any situation where values change over time.
The key idea is simple: measure the difference between the new value and the original value, then compare that difference to the original value.
Percentage Change = ((New Value − Original Value) ÷ Original Value) × 100
Step-by-Step: How to Calculate Percentage Change
- Find the original value (starting number).
- Find the new value (ending number).
- Subtract: new − original to get the change.
- Divide the change by the original value.
- Multiply by 100 to convert to a percent.
Example 1: Percentage Increase
A product price moves from $80 to $100.
- Original = 80
- New = 100
- Change = 100 − 80 = 20
- Change ratio = 20 ÷ 80 = 0.25
- Percentage change = 0.25 × 100 = 25%
The price increased by 25%.
Example 2: Percentage Decrease
A monthly bill drops from $200 to $150.
- Original = 200
- New = 150
- Change = 150 − 200 = -50
- Change ratio = -50 ÷ 200 = -0.25
- Percentage change = -0.25 × 100 = -25%
The bill decreased by 25%.
Percentage Increase vs Percentage Decrease
The sign of your answer tells the story:
- Positive percentage = increase
- Negative percentage = decrease
- 0% = no change
You can also state the direction in words (for example, "increased by 12.5%" or "decreased by 8%") for easier communication.
Common Mistakes to Avoid
- Using the new value as the denominator. Always divide by the original value when calculating percentage change.
- Forgetting to multiply by 100. If your ratio is 0.12, that means 12%, not 0.12%.
- Ignoring negative signs. A negative result means decrease.
- Confusing percentage points with percent change. Going from 10% to 15% is a 5 percentage point increase, but a 50% relative increase.
Special Cases
What if the Original Value Is 0?
Standard percentage change is undefined when the original value is zero, because division by zero is not possible. In practical terms, report the absolute change instead (for example, "increased by 30 units"), or provide context rather than a percent.
What if Values Are Negative?
The formula still works mathematically, but interpretation can become tricky. If negative values are involved (such as profits/losses or temperatures), explain your context clearly and consider using absolute change too.
Where Percentage Change Is Useful
- Comparing prices in shopping or budgeting
- Tracking stock prices and investment returns
- Measuring business growth (sales, users, revenue)
- Analyzing exam scores and grade improvements
- Reviewing health stats (weight, blood markers, performance)
Quick Reference
- Increase: New value is greater than original value
- Decrease: New value is less than original value
- No change: New value equals original value
If you want a fast answer, use the calculator above. If you want to understand the math deeply, practice with a few real examples from your own finances or work data.
Final Thought
Learning percentage change gives you a practical edge: you can interpret trends quickly and make better decisions. Keep the formula handy, focus on the original value as your reference point, and always check whether your result should represent an increase or decrease.