How to calculate a percentage
Choose the calculation you need, then enter two numbers. To find 20% of 250, use 20 × 250 ÷ 100 = 50. To find what percentage 50 is of 250, use 50 ÷ 250 × 100 = 20%.
Percentage change
A move from 80 to 100 is (100 − 80) ÷ |80| × 100 = 25%. A move from 100 to 80 is −20%. The denominator is the absolute starting value, so −80 to −60 is +25% and −80 to −100 is −25%. When the starting value is zero, percentage change is undefined because the formula would divide by zero.
Increase or decrease by a percentage
Increasing 250 by 20% gives 250 × (1 + 20 ÷ 100) = 300. Decreasing it by 20% gives 250 × (1 − 20 ÷ 100) = 200. Negative inputs and percentages are allowed: increasing by −20% has the same mathematical effect as decreasing by 20%. Check what a negative base value means in your particular context.
Input and rounding
Enter a dot as the decimal separator, such as 12.5. Do not enter commas, grouping separators, spaces inside a number, percent signs or expressions. Each input may have up to four decimal places and must be between −1,000,000,000 and 1,000,000,000. Results are rounded to at most six decimal places. A zero denominator or a result beyond the supported range produces a message instead of an invalid number.