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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.
Percentage Calculator: step-by-step worked example
What is 20% of 80? (E.g. a 20% tip on an 80 bill.)
- Calculation type
- Percentage of a number (Y% of X)
- Number
- 80
- Percent (%)
- 20
- 1
Turn the percent into a decimal
Rate = Percent ÷ 100
20 ÷ 100 = 0.2
- 2
Multiply the number by the rate
Result = Number × Percent ÷ 100
80 × 0.2 = 16
- 3
What is left
Remainder = Number − Percentage part (discounted price)
80 − 16 = 64
- 4
Number increased by the percent
Increased = Number + Part = Number × (1 + Rate)
80 × 1.2 = 96
- 20% part1620%
- Remainder6480%
- %54
- %108
- %1512
- %2016
- %2520
- %5040
Good to know: Quick trick: 10% is the number with the decimal point moved one place left; 5% is half of that. Successive discounts do not add up: 20% then 10% off is 28% off (0.8 × 0.9 = 0.72).
Percentage Calculator — how it works
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.
Percentage table: X percent of a number
| Percent | 100 | 250 | 500 | 1,000 | 2,500 | 5,000 | 10,000 |
|---|---|---|---|---|---|---|---|
| %5 | 5 | 12.5 | 25 | 50 | 125 | 250 | 500 |
| %10 | 10 | 25 | 50 | 100 | 250 | 500 | 1,000 |
| %15 | 15 | 37.5 | 75 | 150 | 375 | 750 | 1,500 |
| %18 | 18 | 45 | 90 | 180 | 450 | 900 | 1,800 |
| %20 | 20 | 50 | 100 | 200 | 500 | 1,000 | 2,000 |
| %25 | 25 | 62.5 | 125 | 250 | 625 | 1,250 | 2,500 |
| %30 | 30 | 75 | 150 | 300 | 750 | 1,500 | 3,000 |
| %40 | 40 | 100 | 200 | 400 | 1,000 | 2,000 | 4,000 |
| %50 | 50 | 125 | 250 | 500 | 1,250 | 2,500 | 5,000 |
Frequently asked questions
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.
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About this page
- Publisher:
- Kalkoro — Teknolojig Bilişim Teknolojileri A.Ş., İstanbul
- Written by:
- Ahmet Tur — Editor (Math, date & time, unit conversion, physics & chemistry, everyday tools)
- Reviewed by:
- Kübra Yıldız — Editor
Parameters come from official sources; the last update date is shown at the bottom of the page.
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