$ pct --calculate
Math and conversionPercentage Calculator Online
Five percentage calculations in one place — and each one shows its working, so you can check the reasoning instead of memorising the answer.
- 100% in your browser
- free
- no sign-up
What is a percentage of a value?
Result
Fill in the fields to see the result.
The five calculations and when to use each
Almost every everyday percentage problem is one of these five questions. The confusion is rarely in the arithmetic — it is in choosing which calculation to do. That is why each tab starts with the question in plain language, not with the formula.
- What is X% of Y — the most common one. How much is an 8% commission on a sale, what a 5.2% raise is worth, how much a 30% deposit comes to.
- X is what % of Y — the inverse. How much of your salary goes to rent, your score on a test, what share of the budget an expense consumed.
- Change between two values — comparison over time. From 2,500 to 3,100 is a 24% increase. Works for revenue, price, audience, weight, grades.
- Increase or discount — the final price. What the product costs with 12% off, what the salary becomes after a 4.5% raise.
- Rule of three — pure proportion, with no percentage involved: if 3 kg cost 120, how much do 7 kg cost? It also solves the way back from a discount.
The working is the point
A bare number teaches nothing and cannot be checked. Every mode shows the intermediate steps with your own values — the division by 100, the multiplication, the difference, the quotient. That is what makes the tool usable in an exam, a report or a negotiation: you can reproduce the calculation on paper and explain where the result came from.
If the calculation involves overtime, vacation pay or severance under Brazilian labour law, the percentage is only one step of a larger computation with social security and income tax brackets on top. For those, go straight to the net salary calculator or the severance calculator, which already apply the official 2026 tables.
Three traps that ruin the result
1. Percentages do not add up. A 20% discount followed by a 10% one is not 30% — it is 28%, because the second applies to the already reduced value. To stack them, multiply the factors: 0.80 × 0.90 = 0.72, meaning you pay 72% of the price.
2. The way back is not adding the same percentage. If a value fell by 20%, it has to rise by 25% to return to where it started. Going from 100 down to 80 removes 20 out of 100; going from 80 back up to 100 adds 20 on a smaller base. It is the same reason a 50% drop needs a 100% rise to recover.
3. A percentage of a percentage becomes percentage points. When both numbers are already rates, the difference between them is measured in percentage points. From 5% to 6% is 1 percentage point — and a 20% change. Saying "up 1%" there is wrong in both readings.
Both number formats, pasted straight from a spreadsheet
The calculator understands 1,234.56, 1.234,56 and 1234.56, and discards symbols such as “$”, “%” and spaces. This exists because the same text means two different things: “1.234” is one point two three four in English and one thousand two hundred and thirty-four in Portuguese. When both separators appear together, the last one is always the decimal; when only one appears, the language of the page decides.
Privacy: the maths happens in your browser
No value typed here is sent to any server. All the arithmetic runs locally, in JavaScript, with no network request — which means you can compute margins, salaries, commissions or any sensitive figure without it leaving your machine. The whole page also works offline once loaded.
## faq
Frequently asked questions
How do you calculate a percentage of a value?
Divide the percentage by 100 and multiply by the value. To find 15% of 250: 15 ÷ 100 = 0.15 and 0.15 × 250 = 37.5. The mental shortcut that works for any figure is to start from 10% — just move the decimal point one place to the left (10% of 250 = 25) — and then compose: 15% is 10% plus half of 10%, so 25 + 12.5 = 37.5. In the "What is X% of Y" tab the tool writes out both steps, so you can check the maths instead of trusting the number.
How do you work out what percentage one number is of another?
Divide the part by the total and multiply by 100. If you got 45 out of 180 questions right: 45 ÷ 180 = 0.25 and 0.25 × 100 = 25%. The order matters and that is where almost every mistake happens — the number at the bottom of the division is always the total, the reference whole. A quick sanity check: if the part is smaller than the total, the result must come out below 100%.
How do you apply an increase or a discount in percent?
Work out the amount and add it to or subtract it from the value. A product priced at 899 with a 12% discount: 12% of 899 = 107.88 and 899 − 107.88 = 791.12. A useful check: a 12% discount is the same as paying 88% of the price (899 × 0.88 = 791.12), and a 12% increase is multiplying by 1.12. Working with that factor avoids the classic mistake of applying the percentage to the wrong base when there is more than one step.
Do successive discounts of 20% and 10% add up to 30%?
No — they add up to 28%. Each discount applies to the already reduced value, not to the original price. On 100: the 20% takes you to 80, and the following 10% is worth 8 (10% of 80), not 10 — the final price is 72. The same goes for increases: two 10% rises come to 21%, not 20%. To stack percentages, multiply the factors (0.80 × 0.90 = 0.72) instead of adding the percentages.
How do you find the price before the discount?
Divide by the factor, do not add the percentage back — that is the classic error. If a product sold for 791.12 after a 12% discount, the original price is 791.12 ÷ 0.88 = 899. Adding 12% to 791.12 would give 886.05, which is wrong, because the original 12% was calculated on a larger value. In the tool, the "Rule of three" tab solves this directly: 88 is to 791.12 as 100 is to X.
What is the difference between percentage change and percentage points?
A percentage point is the absolute difference between two percentages; percentage change is how much one grew relative to the other. If a rate goes from 5% to 6%, the rise is 1 percentage point — but 20% in percentage change (1 ÷ 5 = 0.20). Both numbers describe the same fact and are not interchangeable: headlines swap one for the other precisely because "up 20%" sounds bigger than "up 1 point". Use percentage points when both values are already percentages.
How does the rule of three work?
Set up the proportion and cross-multiply. If 3 kg cost 120, how much do 7 kg cost? Multiply the crossed values and divide by the remaining one: (120 × 7) ÷ 3 = 280. That holds for directly proportional quantities, where one grows along with the other. When the relationship is inverse — more people, less time to finish the same task — the maths changes: multiply the first two values and divide by the third. The tool offers both, and picking the wrong one is what most often produces an absurd result.
Which number formats does the calculator accept?
You can type 1,234.56 (international format), 1.234,56 (Brazilian format) or 1234.56 — the tool works out which separator is the decimal one and reads the value correctly. Symbols such as "$", "%" and spaces are ignored too, so pasting a value straight from a spreadsheet or a website works without cleaning up the text first.
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