Percentage Calculator
Quickly compute percentages, percentage change, increases, discounts, and common ratios with exact mathematical step-by-step working.
How to Think About Percentages
A percentage is just a fraction out of 100. For example, 15% means 15 out of every 100, or 0.15 in decimal form. When calculating percentage change, you compare the absolute difference between your new and old numbers against where you started: ((New - Old) ÷ Old) × 100%.
Frequently Asked Questions
How do you calculate a percentage of a number?
Convert the percentage to a decimal by dividing by 100, then multiply by the number. For example, to find 20% of 150: (20 ÷ 100) × 150 = 0.20 × 150 = 30.
How do you calculate percentage increase or decrease?
Subtract the old value from the new value, divide by the absolute value of the original number, and multiply by 100: ((New - Old) ÷ |Old|) × 100. If positive, it is an increase; if negative, it is a decrease.
What is the formula to find what percent X is of Y?
Divide the part (X) by the whole (Y) and multiply by 100: (X ÷ Y) × 100%. For example, 25 out of 200 is (25 ÷ 200) × 100% = 12.5%.
How do you calculate a discount or sales tax?
To add tax or markup: Original × (1 + Rate ÷ 100). To subtract a discount: Original × (1 - Discount ÷ 100). For example, a 15% discount on $80 is 80 × (1 - 0.15) = 80 × 0.85 = $68.