Four percentage calculators in one
Percentages are everywhere: discounts, taxes, grades, sales growth and pay rises. Instead of looking up the formula every time, this page combines the four most common calculations and shows the working so you learn it too.
1. What is X% of Y?
Example: 15% of 200 = 15 ÷ 100 × 200 = 30. Use it for discounts, tax or commission amounts.
2. X is what percent of Y?
Example: you scored 30 out of 120: 30 ÷ 120 × 100 = 25%.
3. Percentage change
Example: a price rises from 80 to 100: (100 − 80) ÷ 80 × 100 = 25% increase. Falling from 100 to 80 is a 20% decrease, not 25%, because the base changed.
4. Increase or decrease by a percent
Example: 250 with 20% off: the discount is 50, final price 200. A salary of 250 raised by 20% becomes 300.
Common mistakes
- Adding successive percentages: 20% then 10% off equals 28%, not 30%. Use our Discount Calculator for stacked discounts.
- Points vs percent: going from 10% to 12% is +2 percentage points but a 20% relative increase.
- Wrong base: percentage change is always relative to the original value.