Percentage Change Calculator
The Percentage Change Calculator shows how much a value has increased or decreased as a percentage of its original value. Enter the original value (the amount before the change) and the new value (the amount after the change), and it tells you the change as a percentage. It is useful whenever you need to compare a before-and-after number — a price, salary, score, measurement or business metric — in relative terms.
Percentage Change Calculator
What the result means
The result is the size of the change relative to the original value. A positive percentage means the value increased — the new value is larger than the original. A negative percentage means the value decreased — the new value is smaller than the original. For example, +18.75% means the new value is 18.75% larger than the original, while −15.79% means it is 15.79% smaller. A result of 0% means the two values are the same.
How to use this calculator
- 1Enter the original value — the amount before the change.
- 2Enter the new value — the amount after the change.
- 3Press Calculate to see the percentage change, the absolute change, and whether it is an increase or a decrease.
- 4Try swapping the two values to see how the reference point changes the result.
The formula
Percentage change answers one question: how big is the change from the original value, compared with the original value itself? Both common forms of the standard formula are:
What each variable means
| Symbol | Name | Description |
|---|---|---|
| Original | Original value | The starting value before the change. This is the reference point the change is measured against. |
| New | New value | The value after the change. |
Step-by-step example
Percentage increase: from 80 to 95
- 1Difference = New − Original = 95 − 80 = 15
- 2Percentage change = (15 ÷ 80) × 100 = 18.75%
- 3The result is positive, so the value increased.
Result
The value increased by 18.75%.
What changes the result
- The result is always measured against the original value, so the same absolute change gives a different percentage for different starting points.
- Swapping the two values changes the result: 80 → 95 is +18.75%, but 95 → 80 is −15.79%. They are not simply +X% and −X% because the original value (the denominator) changes.
- A smaller original value makes the same absolute change look larger as a percentage.
- When the original value is zero, the percentage cannot be calculated — dividing by zero is undefined.
Edge cases to be aware of
Unusual situations handled correctly
- If the original value is 0 and the new value differs, percentage change is undefined. The formula divides by the original value, and division by zero has no answer — so the calculator shows “Undefined†instead of a number.
- If the original value equals the new value, the result is 0%: nothing changed.
- Decimal values work normally. For example, a change from 12.5 to 15 gives (2.5 ÷ 12.5) × 100 = 20%.
- Negative values are accepted, but the sign only has its usual increase/decrease meaning when the original value is positive. With a negative original value the result can carry an unexpected sign, so interpret it with care.
Common mistakes
Avoid these errors
- Using the new value as the denominator. Percentage change always divides by the original value.
- Treating a change as reversible: a 50% increase (100 → 150) needs a 33.3% decrease (150 → 100) to return to the start, not 50%.
- Confusing percentage change with percentage difference. Percentage difference compares two values symmetrically; percentage change treats the original value as the reference.
- Misreading the sign when the original value is negative — the usual “positive = increase†rule can break.
Assumptions
- The original value is the reference point for the calculation.
- Both values use the same unit or scale.
Limitations
- For very small original values, even a small absolute change can produce a very large percentage, which can be misleading without context.
- When the original value is zero, no percentage change exists.
Real-world scenarios
Percentage decrease: from 95 to 80
Suppose a product's price fell from 95 to 80.
What it means: Difference = 80 − 95 = −15. Percentage change = (−15 ÷ 95) × 100 = −15.79%. The negative result shows the price decreased by 15.79%. Notice this is not the reverse of 80 → 95 (+18.75%): each change is measured against its own original value.
Salary increase
A monthly salary grows from ₹40,000 to ₹45,000.
What it means: Difference = 5,000. Percentage change = (5,000 ÷ 40,000) × 100 = 12.5%. The salary increased by 12.5% compared with the original salary.
Sales growth
Monthly sales rise from 200 units to 240 units.
What it means: Difference = 40. Percentage change = (40 ÷ 200) × 100 = 20%. Sales grew by 20% relative to the original 200 units.
Investment value
An investment is worth ₹1,00,000 at the start of the year and ₹1,08,000 at the end.
What it means: Difference = 8,000. Percentage change = (8,000 ÷ 1,00,000) × 100 = 8%. The investment grew by 8% over the year.
Test score improvement
A student's score improves from 60 to 75.
What it means: Difference = 15. Percentage change = (15 ÷ 60) × 100 = 25%. The score improved by 25% relative to the original 60.
Related concepts
Finds what a percentage of a given value is — for example, 20% of 150. Percentage of a number starts from a percentage; percentage change starts from two values and finds the percentage.
Percentage difference
Compares two values symmetrically, without treating either one as the “originalâ€. It divides the absolute difference by the average of the two values, so the result is the same no matter which value you enter first.
Percentages, fractions and decimals are three ways to write the same relationship. Convert between them when you need to use a percentage in further calculations.
A discount is a percentage decrease applied to a price. Use the discount calculator to find the sale price and total savings from a discount percentage.