How do you calculate a percentage?
To calculate X% of a value Y, multiply Y by X and divide by 100. Example: 20% of 150 = 150 × 20 ÷ 100 = 30.
Calculating a percentage increase
The change between a start value A and an end value B is: (B − A) ÷ A × 100. A positive result means an increase, negative a decrease.
Frequently asked questions
How do I calculate a discount?
Final price = original price × (1 − discount ÷ 100). For 30% off 80: 80 × 0.70 = 56.
How do I find the price before a discount?
Divide the sale price by (1 − discount ÷ 100). E.g. 56 after −30% → 56 ÷ 0.70 = 80.