Percentage increase and decrease trip up a lot of people, but the formula is simple once you see it broken down. You can work it out by hand below, or use our free Percentage Calculator for an instant answer.
The Formula
Percentage change compares an original value to a new value, expressed as a percentage of the original:
Percentage Change = ((New Value − Original Value) ÷ Original Value) × 100
A positive result means an increase. A negative result means a decrease.
Worked Example: Percentage Increase
Say a product’s price rose from $80 to $100.
- New Value − Original Value = 100 − 80 = 20
- 20 ÷ 80 = 0.25
- 0.25 × 100 = 25%
- Result: a 25% increase
Worked Example: Percentage Decrease
Say a value dropped from 120 to 90.
- New Value − Original Value = 90 − 120 = −30
- −30 ÷ 120 = −0.25
- −0.25 × 100 = −25%
- Result: a 25% decrease
The Most Common Mistake
The most common error is dividing by the new value instead of the original value. Percentage change is always relative to where you started, not where you ended up — always divide by the original value.
Skip the Math
Our free Percentage Calculator handles percentage increase, decrease, and two other common percentage problems instantly — no formulas to remember.
Frequently Asked Questions
How do I know if it’s an increase or a decrease?
If the result of the formula is positive, it’s an increase. If it’s negative, it’s a decrease.
What’s the fastest way to calculate percentage change?
Use the free Percentage Calculator tool — enter your original and new values and it calculates the percentage change instantly.
