Overview
Percentage change measures how much a value increased or decreased relative to its original value. It is useful for comparing prices, results and performance before and after.
Formula
Change % = (new value − old value) ÷ |old value| × 100
How it works
Subtract the old value
Find the difference: new value minus old value.
Divide by the old value
Use the absolute old value to keep the direction correct.
Multiply by 100
Convert to a percentage, then read it as an increase or decrease.
Worked examples
Example 1: increase
From 200 to 250: (250 − 200) ÷ 200 × 100 = 25% increase.
Example 2: decrease
From 500 to 400: (400 − 500) ÷ 500 × 100 = −20%, a 20% decrease.
Frequently asked questions
What is the difference between percentage change and percentage difference?
Percentage change compares a new value with an old value, while percentage difference compares two values without a time order and uses their average in the denominator.
What if the old value is zero?
Division by zero is undefined, so percentage change cannot be calculated when the old value is zero.
Does 20% mean an increase or a decrease?
The sign tells you: positive is an increase and negative is a decrease. The calculator shows the direction clearly.
Can I use it for prices?
Yes. It is one of the most common ways to compare prices before and after a discount or inflation.
This calculator is for educational and informational purposes only and is not a substitute for professional advice.