Percentages are everywhere — discounts, tax, tips, interest, exam scores. But there isn't one "percentage calculation"; there are four distinct questions, and mixing them up gives the wrong answer.
Percentage of a number (Y% of X)
Multiply the number by the percent and divide by 100: 18% of 850 = 850 × 18 ÷ 100 = 153.
What percent is X of Y?
Divide the part by the whole and multiply by 100: 45 out of 360 is 45 ÷ 360 × 100 = 12.5%. This is the mode for exam scores and shares of a total.
Percentage increase and decrease
Difference divided by the starting value, times 100: from 80 to 95 is (95 − 80) ÷ 80 × 100 = +18.75%. A negative result means a decrease.
The most common mistake: adding percentages
Percentages don't add — they multiply. A 20% increase followed by a 20% discount does not return to the start: 100 → 120 → 96. In chained discounts, each step applies to the previous result.
Do all of these in one place with the Percentage Calculator.