How to Calculate a Percentage (3 Everyday Formulas)
Learn how to find a percentage of a number, what percent one value is of another, and percentage change — with simple formulas and worked examples.
To find X% of a number, multiply the number by X and divide by 100. For example, 15% of 200 is 200 × 15 ÷ 100 = 30. Most everyday percentage questions come down to three formulas below.
1. What is X% of Y?
Multiply, then divide by 100:
- Formula: result = Y × X ÷ 100
- Example: 20% of 150 = 150 × 20 ÷ 100 = 30
This is the calculation behind discounts, tips and tax.
2. X is what percent of Y?
Divide the part by the whole and multiply by 100:
- Formula: percent = X ÷ Y × 100
- Example: 50 out of 200 = 50 ÷ 200 × 100 = 25%
Use it for scores, completion rates and shares.
3. Percentage increase or decrease
Compare the new value to the old:
- Formula: change = (new − old) ÷ old × 100
- Example: 120 → 150 = (150 − 120) ÷ 120 × 100 = +25%
A positive result is growth, a negative result is a drop.
Skip the arithmetic
The percentage calculator handles all three cases at once, live in your browser. Working with money instead? See how repayment maths works in How loan EMI is calculated.