Percentages show up everywhere — discounts, tips, test scores, price changes — and almost every real question is one of three types. Learn the method for each and you can handle nearly any percentage problem without reaching for a calculator.
TL;DR — Pick the question type in the percentage calculator, enter two numbers, and read the answer.
1. What is X% of Y?
This is finding a share of a number. Convert the percent to a decimal by dividing by 100, then multiply. 15% of 200 is 0.15 × 200 = 30. This covers tips, sales tax, commissions and discounts — anything where you take a slice of a total.
2. X is what percent of Y?
This turns two numbers into a ratio. Divide the part by the whole and multiply by 100. 30 is what percent of 200? 30 ÷ 200 = 0.15, or 15%. Use it for test scores, completion rates, and “how much of my budget did this take” questions.
3. Percent change from A to B
This measures how much something grew or shrank. Subtract the old value from the new, divide by the old value, and multiply by 100. From 200 to 250: (250 − 200) ÷ 200 = 0.25, a 25% increase. A negative result means a decrease. This is the one for price changes, growth rates and before-and-after comparisons.
Run any of the three in the percentage calculator — it switches between them so you never have to remember which formula goes where.