Percentage formulas
A percentage is a number expressed as a fraction of 100. These four formulas cover almost every everyday percentage question:
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | Y × X ÷ 100 | 15% of 80 = 12 |
| X is what % of Y? | X ÷ Y × 100 | 12 is 15% of 80 |
| % change from X to Y | (Y − X) ÷ |X| × 100 | 50 → 65 = +30% |
| Increase X by Y% | X × (1 + Y ÷ 100) | 200 + 10% = 220 |
Everyday uses
- Discounts: 25% off a $60 item saves $15, so you pay $45.
- Tips: a 20% tip on a $45 bill is $9.
- Pay rises: a raise from $3,000 to $3,150 a month is a 5% increase.
- Grades: 42 correct answers out of 50 is 84%.
- Sales tax and VAT: adding 8% tax to $50 gives $54.
