Formula & method
X% of Y = (X ÷ 100) × Y. X as a percentage of Y = (X ÷ Y) × 100. Percent change = ((new − old) ÷ old) × 100.
Worked example
20% of 150 is 30. 30 as a percentage of 150 is 20%. A price rising from $80 to $100 is a 25% increase.
FAQ
- How do I add a percentage to a price?
- Multiply the price by (1 + percentage ÷ 100). Adding 8% tax to $50 gives $50 × 1.08 = $54.
- How do I reverse a percentage?
- To find the original price after a 20% discount to $80, divide: $80 ÷ 0.80 = $100.
- What is the difference between percent and percentage points?
- A rise from 10% to 15% is 5 percentage points, but a 50% relative increase.
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