Math guides
How to Calculate Percentages
Every percentage formula you'll ever need — percentage of a number, increase, decrease, reverse percentages, tips and discounts — explained in plain English with worked examples you can follow step by step.
Frequently asked questions
How do I calculate a percentage of a number?
Convert the percentage to a decimal by dividing by 100, then multiply by the number. For example, 25% of 80 is 0.25 × 80 = 20.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, then multiply by 100. If a price rises from $40 to $50: (50 − 40) ÷ 40 × 100 = 25% increase.
How do I calculate percentage decrease?
Subtract the new value from the old value, divide by the old value, then multiply by 100. If a price drops from $50 to $40: (50 − 40) ÷ 50 × 100 = 20% decrease.
How do I reverse a percentage to find the original number?
Divide the final value by 1 plus the percentage as a decimal. If a shirt costs $30 after a 25% discount, the original price was 30 ÷ 0.75 = $40.