Common Percentage Calculations
What is X% of Y?
Formula: (X / 100) x Y
Example: 15% of 200 = 30
X is what % of Y?
Formula: (X / Y) x 100
Example: 30 is 15% of 200
Percentage Change
Formula: ((New - Old) / Old) x 100
Example: 100 to 125 = +25%
Discount
Formula: Price - (Price x Discount%)
Example: $100 - 20% = $80
When Do You Need Percentage Calculations?
- Shopping - calculating sale prices and discounts
- Business - profit margins, markups, and commissions
- Finance - interest rates, returns, and growth
- Taxes - calculating tax amounts and deductions
- Tips - figuring out gratuity at restaurants
Quick mental math: To calculate 10% of any number, just move the decimal point one place to the left. For 20%, calculate 10% and double it. For 15%, add 10% and half of 10%.