Percentage Change Calculator
Use this quick tool to calculate percentage increase or decrease between an old value and a new value.
Formula: ((New Value - Old Value) / Old Value) × 100
What Is Percentage Change?
Percentage change tells you how much something has increased or decreased relative to its original amount. It is one of the most useful concepts in finance, business, education, fitness tracking, and everyday decisions. If a price goes from $50 to $65, or your monthly website traffic goes from 10,000 visits to 12,500 visits, percentage change shows the change in a standardized way.
Instead of just saying the value changed by “15” or “2,500,” percentage change lets you compare changes across different scales. That is why it is commonly used in stock returns, inflation rates, sales growth, and score improvements.
Percentage Change Formula
The standard formula is:
- Percentage Change = ((New Value - Old Value) / Old Value) × 100
The sign of your answer matters:
- Positive result = percentage increase
- Negative result = percentage decrease
- Zero = no change
How to Calculate Percentage Change Step by Step
1) Identify your old and new values
The old value is your starting point. The new value is the updated value.
2) Subtract old from new
This gives the absolute change.
- Absolute Change = New − Old
3) Divide by the old value
This scales the change compared to where you started.
4) Multiply by 100
Convert the decimal into a percentage.
Examples
Example 1: Percentage Increase
A product price rises from 80 to 100.
- Change = 100 − 80 = 20
- 20 / 80 = 0.25
- 0.25 × 100 = 25%
Result: 25% increase
Example 2: Percentage Decrease
Monthly spending drops from 250 to 200.
- Change = 200 − 250 = -50
- -50 / 250 = -0.2
- -0.2 × 100 = -20%
Result: 20% decrease
Example 3: No Change
If the old and new values are both 45:
- Change = 45 − 45 = 0
- 0 / 45 = 0
- 0 × 100 = 0%
Result: no percentage change
Common Mistakes to Avoid
- Using the new value in the denominator: use old value for standard percentage change.
- Forgetting to multiply by 100: decimal 0.18 means 18%.
- Ignoring the sign: negative means decrease, positive means increase.
- Confusing percentage change with percentage points: they are not the same.
Percentage Change vs. Percentage Points
If an interest rate moves from 4% to 6%, that is:
- +2 percentage points (6% − 4%)
- +50% percentage change because 2 ÷ 4 = 0.5
This distinction is very important in finance and news reporting.
What If the Old Value Is Zero?
If the old value is 0 and the new value is not 0, standard percentage change is undefined because division by zero is impossible. In that case, report the absolute change or choose a different baseline.
If both old and new are 0, the change is effectively 0.
Quick Reference
- Increase: new value higher than old value
- Decrease: new value lower than old value
- Formula: ((New − Old) / Old) × 100
- Use old value as baseline
Final Thoughts
Once you learn the formula, calculating percentage change becomes straightforward. Use the calculator above whenever you need a fast answer, and follow the step-by-step method when solving manually. Whether you are analyzing investment returns, budget changes, exam scores, or business growth, percentage change helps you make clearer comparisons and better decisions.