Percentage Change Calculator
Percentage change tells you how far a number moved relative to where it started. Enter the original value and the new value, and this calculator reports the increase or decrease as a percentage, along with the plain difference between the two. It is the right tool for tracking a price rise, a salary bump, a weight loss, a stat that went up or down between two periods, or any before-and-after comparison where the size of the move matters more than the raw numbers.
Calculate
Default result: 25.00
Percentage Change Calculator · Result
calculators.dev
Percent change
80 × 100
- Difference
- 20.00
Reviewed by the calculators.dev team · Last updated 2026-06-23
How to calculate
Type the original value first, then the new value. The calculator subtracts the original from the new to get the difference, divides that difference by the original, and multiplies by 100 to express the move as a percentage. A positive answer is an increase and a negative answer is a decrease. Going from 80 to 100, for instance, is a 20-unit rise on a base of 80, which is a 25% increase. The result refreshes as you type so you can compare several before-and-after pairs in a row.
percent change = ((new value − old value) ÷ old value) × 100. The difference (new − old) is divided by the original value, not the new one, because the change is measured against where the number started. A result above zero is growth; below zero is a drop. The raw difference (new − old) is also shown so you can see the absolute size of the move.
Example calculation
Going from 80 up to 100 adds 20. Dividing that 20 increase by the original 80 and multiplying by 100 gives a 25% rise. The calculator reports both the +25% change and the +20 raw difference.
- percentChange
- +25%
- difference
- +20
Assumptions
- The change is always measured against the ORIGINAL value, so the same absolute move is a larger percentage when the starting number is smaller.
- The original value cannot be zero, because a change measured from nothing has no defined percentage.
- A percentage decrease can never exceed −100% for a value that stays positive, since the number cannot fall below zero by dropping more than its whole.
Common mistakes
- Dividing by the new value instead of the original — this is the single most common percentage-change error and it skews both increases and decreases.
- Confusing percentage change with percentage points: going from 10% to 15% is a 5 percentage-point rise but a 50% change.
- Assuming a 50% drop followed by a 50% rise returns to the start — it does not, because each percentage is taken against a different base.
Frequently asked questions
What is the percentage change from 80 to 100?
It is a 25% increase. The value rose by 20, and 20 ÷ 80 = 0.25, which is 25%.
How do I calculate a percentage decrease?
Use the same formula — ((new − old) ÷ old) × 100. When the new value is smaller, the result comes out negative, which represents the decrease.
What is the difference between percentage change and percentage points?
Percentage points are the plain gap between two percentages. Percentage change measures that gap relative to the starting percentage, so 10% to 15% is 5 points but a 50% change.
Why can’t the original value be zero?
The formula divides by the original value, and dividing by zero is undefined, so a change starting from zero cannot be expressed as a percentage.