How percentage calculator works
This calculator handles the two most common percentage tasks. The first finds a percentage of a number: to calculate X% of Y, multiply Y by X and divide by 100. For example, 15% of 80 is 80 × 15 ÷ 100 = 12. This is useful for discounts, tips, taxes, and commissions.
The second calculates the percentage change between two values — the difference divided by the original, multiplied by 100. A change from 40 to 50 is an increase of 25%, because (50 − 40) ÷ 40 × 100 = 25. The result is shown as a positive percentage for increases and a negative one for decreases.
Both calculations are exact to six decimal places and run instantly in your browser. There's no rounding surprise and no data sent anywhere — handy when you're quickly checking a sale price, a pay rise, or how much something has grown or shrunk.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 20% of 50 is 50 × 20 ÷ 100 = 10. The first calculator above does this instantly — enter the percentage and the value and click Calculate.
How do I work out percentage increase or decrease?
Subtract the original from the new value, divide by the original, then multiply by 100. A positive result is an increase; a negative result is a decrease. Use the second calculator and enter the original (From) and new (To) values.
What is the formula for percentage change?
Percentage change = ((new − original) ÷ original) × 100. The calculator applies this exactly and shows whether the change is an increase or a decrease.
Can I calculate reverse percentages?
Yes, indirectly. If a value is the result of adding a percentage to an original, divide by (1 + percentage/100) to find the original. For example, if 120 includes 20% added, the original is 120 ÷ 1.2 = 100.
