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Percentages run through everyday life — 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: finding a percentage of a number, finding what percent one number is of another, finding a percentage change, and adding or subtracting a percentage.
Pick the question you're asking, enter the numbers, and get the answer instantly.
How is it calculated?
The four percentage questions
| Question | Formula | Example |
|---|---|---|
| Y% of X | X × Y ÷ 100 | 18% of 850 = 153 |
| X is what % of Y | X ÷ Y × 100 | 45 is 12.5% of 360 |
| Change from X to Z | (Z − X) ÷ X × 100 | 80 → 95 = +18.75% |
| Add / subtract Y% | X × (1 ± Y ÷ 100) | 200 + 20% = 240 |
The most common mistake: chaining percentages
Percentages don't add — they multiply. A 20% increase followed by a 20% discount does not bring you back to the start: 100 → 120 → 96. Likewise a value that drops 50% then rises 50% does not return to its original (100 → 50 → 75). In chains like discount-on-discount, each step applies to the previous result.
Percentage points ≠ percent
When a rate goes from 10% to 12%, saying it "rose 2%" is wrong: that's a 2 percentage-point rise, but the relative increase is 20% (2 ÷ 10). This is the distinction most often confused in news and finance.
Where it helps
Finding a sale price, working out a raise as a percentage, computing exam success rates, or a line item's share of a total. For sales tax use a dedicated VAT calculator; for pay raises use a raise calculator.
Worked example
Say an item costs 850 and you're adding 20% sales tax: 850 × 20 ÷ 100 = 170 tax, total 1,020. Now suppose the same item first gets a 20% markup (to 1,020) then goes into a "20% off" sale — the price falls to 816, below the original 850, because the discount is taken on the marked-up price. That's the classic illustration that percentages don't add: each step applies to the previous result, not the original.
FAQ
How do I find the percentage of a number?+
Multiply the number by the percent and divide by 100: 18% of 850 = 850 × 18 ÷ 100 = 153. Just pick the "Percentage of a number" mode in the tool.
How do I find what percent one number is of another?+
Divide the part by the whole and multiply by 100: 45 out of 360 = 45 ÷ 360 × 100 = 12.5%. This is the mode for exam scores and shares of a total.
How is percentage increase or decrease calculated?+
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.
Why don't percentages add up?+
Because each percentage applies to the previous result. A value that rises 20% then falls 20% does not return to the start (100 → 120 → 96); in chained discounts or markups you must calculate each step in order.
What is the difference between percent and percentage points?+
If a rate goes from 10% to 12%, that is a 2 percentage-POINT rise, but a 20% relative increase (2 ÷ 10). "Points" describe the absolute gap; "percent" describes the relative change.
Which mode do I use to add tax or a markup?+
The "Add / subtract a percentage" mode: 200 plus 20% is 200 × 1.20 = 240. For sales tax specifically, a dedicated VAT calculator has the rates built in.