How to Calculate Percentage
A percentage is a number or ratio expressed as a fraction of 100. The symbol % means “per hundred.” This guide explains the main percentage formulas and how to use them with step-by-step examples.
1. What is X% of Y?
To find what X percent of Y is, multiply Y by X and divide by 100.
Formula: (X ÷ 100) × Y
Example: What is 20% of 150?
(20 ÷ 100) × 150 = 0.2 × 150 = 30
2. X is what percent of Y?
To find what percentage X is of Y, divide X by Y and multiply by 100.
Formula: (X ÷ Y) × 100
Example: 30 is what percent of 150?
(30 ÷ 150) × 100 = 0.2 × 100 = 20%
3. Percentage Increase
When a value goes from an old value to a new value, the percentage increase is:
Formula: ((New − Old) ÷ Old) × 100
Example: Price increased from 50 to 75.
((75 − 50) ÷ 50) × 100 = (25 ÷ 50) × 100 = 50% increase
4. Percentage Decrease
When a value decreases from old to new:
Formula: ((Old − New) ÷ Old) × 100
Example: Price dropped from 80 to 60.
((80 − 60) ÷ 80) × 100 = (20 ÷ 80) × 100 = 25% decrease
5. Add or Subtract a Percentage
Add X% to a value: Value + (Value × X ÷ 100)
Subtract X% from a value: Value − (Value × X ÷ 100)
Example (add 15% to 200): 200 + (200 × 15 ÷ 100) = 200 + 30 = 230
Quick reference
- What is X% of Y? → (X/100) × Y
- X is what % of Y? → (X/Y) × 100
- Increase → ((new − old)/old) × 100
- Decrease → ((old − new)/old) × 100