How percentage calculator works
This calculator handles the three 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. A third panel answers the reverse question directly: given a part and a whole, it shows the part as a percentage of the whole (12 is 15% of 80).
Both calculations are exact to six decimal places and run instantly in your browser. All three panels share the same engine — 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.