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Percentage Calculator
To find 15% of 80, divide 15 by 100 to get 0.15 and multiply by 80: the answer is 12. To find what percent 12 is of 80, divide 12 by 80 and multiply by 100: 15%. To find the whole when 12 is 15%, divide 12 by 0.15: 80. This calculator does all three, exactly.
Part, whole and percent: find any one.
- 15% means 15 per hundred: 15 ÷ 100 = 0.15.
- Multiply by the number: 0.15 × 80 = 12.
- Check: 12 ÷ 80 × 100 = 15%.
| Result | Value |
|---|---|
| 15% of 80 | 12 |
| As a fraction | 3/20 of 80 |
| The decimal multiplier | 0.15 |
| Swapped, the same answer | 80% of 15 = 12 |
| 80 minus 15% | 68 |
| 80 plus 15% | 92 |
The figures above are an example: put in your own. Choose the question, then type whole numbers, decimals (0.5 or 0,5), thousands with commas (1,500) or a fraction such as 33 1/3. Splitting a whole tally into percentages that add to 100? Use the tally percentage calculator. Worked out exactly in this browser and kept there; nothing is sent anywhere.
Choose the question, type the two numbers you know and read the third, with the working and a check. Answers are exact; anything that repeats, like 1 of 3 as 33.(3)%, is shown both rounded and exact.
A percentage is a number expressed as a part of 100: 15% means 15 per hundred, or 0.15. A percentage calculator finds a percent of a number, what percent one number is of another, or the whole when a part and its percent are known.
- No sign-up
- Nothing uploaded
- Shows every step
- Works offline
- Exact, no rounding errors
Key facts
| Detail | Answer |
|---|---|
| Questions | P% of Y; X is what % of Y; X is P% of what |
| Example | 15% of 80 = 12; 12 of 80 = 15%; 12 is 15% of 80 |
| Formula | Part = percent ÷ 100 × whole |
| Accepts | 15, 0.5, 0,5, 1,500, -3, 33 1/3 |
| Rounding | 0 to 10 decimal places, half away from zero; exact value shown too |
| Where your numbers are kept | This browser only |
How to work out a percentage of a number
The same three steps the calculator shows, which also work on paper.
Pick the question
A percent of a number, what percent one number is of another, or the whole.
Enter what you know
The labels change with the question, so each box says what goes in it.
Turn the percent into a decimal
Divide by 100: 15% is 0.15.
Multiply or divide
Multiply by the whole to get the part; divide the part by it to get the whole.
Read the check
The last step turns the answer back into the question.
Choose the rounding
Pick the decimal places; the exact value stays visible.
Who uses a percentage calculator
Anyone with two of the three numbers and a question about the third.
Shoppers
What 25% off takes off a price, and what is left to pay, with a price in another currency changed first on the currency converter.
Students
Homework checked against the steps, not just the answer.
Restaurant bills
A tip as a percent, or the percent a given tip works out to.
Teachers and coaches
18 of 24 pupils present is 75%.
Small businesses
A deposit of 15% and the total it implies.
People with counts
A count turned into its share of a total.
Part, whole and percent: which number is which
Every everyday percentage question has three numbers in it: a part, a whole and a percent. You always know two and want the third, and the only real difficulty is deciding which number is the whole. The whole is the thing the percentage is “of”: the price before the discount, the class size, the number of shots taken. Once that is fixed, the formula picks itself.
| Question | You know | Formula | Example |
|---|---|---|---|
| What is 15% of 80? | Percent and whole | Part = percent ÷ 100 × whole | 0.15 × 80 = 12 |
| 12 is what percent of 80? | Part and whole | Percent = part ÷ whole × 100 | 12 ÷ 80 × 100 = 15% |
| 12 is 15% of what? | Part and percent | Whole = part ÷ (percent ÷ 100) | 12 ÷ 0.15 = 80 |
These are the same equation, part = rate × whole, solved for a different unknown. The US Common Core standards put it the same way for Grade 6: find a percent of a quantity as a rate per 100 (30% of a quantity means 30/100 times the quantity), and solve problems that find the whole given a part and the percent (standard 6.RP.A.3c). The calculator above is that standard as three buttons, with the check written out underneath so you can see the three framings agree.
A useful test when a question is worded awkwardly: rewrite it as “___ is ___% of ___” and fill in what you know. “A 12-dollar tip on an 80-dollar bill” becomes “12 is ?% of 80”. “Pay 15% deposit, the deposit was 12” becomes “12 is 15% of ?”.
Why 8% of 50 is the same as 50% of 8
Percentages of a number can be swapped round: P% of Y is always the same as Y% of P, because both are P × Y ÷ 100. That turns hard mental sums into easy ones. 8% of 50 looks awkward; 50% of 8 is obviously 4, and that is the answer to both.
| Hard way round | Easy way round | Answer |
|---|---|---|
| 8% of 50 | 50% of 8 | 4 |
| 16% of 25 | 25% of 16 | 4 |
| 4% of 75 | 75% of 4 | 3 |
| 18% of 50 | 50% of 18 | 9 |
| 12% of 250 | 250% of 12 (12 × 2.5) | 30 |
| 7% of 300 | 300% of 7 (7 × 3) | 21 |
The calculator shows the swapped version in its table for every “what is P% of” question. Two other mental shortcuts: 10% is the number with the decimal point moved one place left (10% of 80 is 8), so 5% is half of that and 15% is the two added together (8 + 4 = 12). And 1% is the point moved two places, which builds any percent a piece at a time.
20% off then 10% off is not 30% off
Three mistakes account for most wrong percentage answers. None of them is an arithmetic slip; each is a wrong choice of whole.
| Question | Wrong answer | Right answer | Why |
|---|---|---|---|
| A shirt is 20% off, then a further 10% off | 30% off | 28% off | The second 10% comes off the already reduced price: 0.8 × 0.9 = 0.72 |
| Prices rose 50%, then fell 50% | Back where they started | 25% lower | 1.5 × 0.5 = 0.75 of the original |
| A price of 120 includes 20% tax; the tax is | 24 | 20 | The tax is 20% of the price before tax (100), not of 120 |
| 45 of 50 in one group agree (90%) and 30 of 150 in another (20%): overall | 55%, the average of 90 and 20 | 37.5% | Add the counts and the totals: 75 of 200. Groups of different sizes cannot be averaged as percentages |
Stock accuracy is a percentage too: 20 of 22 counts within tolerance is a 90.9% hit rate, one of the two accuracy scores cycle counting tracks.
The last row matters on a counting site: percentages of different totals cannot simply be averaged. Combine the counts and the totals, then divide once; volleyball’s team hitting percentage is worked the same way, from team totals, as volleyball hitting percentage and stats shows. The average calculator’s section on averaging averages works through why, and the percentage increase calculator handles the tax case directly.
What this calculator does not do
This page answers one percentage question at a time. For a full tally (several categories counted, each turned into a percentage of the total so they add to exactly 100), use the tally percentage calculator, which handles the rounding that makes 33% + 33% + 33% come to 99. For a change between two values, the percentage change calculator separates percent change from percentage points. To type a whole sum with a percent key, such as 48.50 + 15%, the online calculator follows the convention most handheld calculators use.
| Topic | What this calculator does |
|---|---|
| Inputs | Whole numbers, decimals, negatives, thousands with commas, decimal commas, fractions and mixed numbers (33 1/3) |
| Arithmetic | Exact: every number is kept as a fraction of two whole numbers, so nothing is lost before the final rounding |
| Rounding | Half away from zero, to the places you choose (0 to 10); the exact value is shown beside it when they differ |
| Refuses | A whole of 0 (“what percent of 0”) and a percent of 0 when finding the whole, with a message |
| Does not | Compound interest, tax rules, tips by country, or anything that needs a rate that changes over time |
Taking VAT out of a price: the fraction HMRC uses
The commonest percentage slip on a UK receipt or invoice is taking 20% off a price that already includes VAT. HMRC’s VAT guide, Notice 700, section 7.3.1, gives the right tool, the VAT fraction: the rate divided by 100 plus the rate, so 20/120, one sixth, at 20%. Its example: on a sale of £2.40 at 20%, the VAT is 40p, which “is not 20% of £2.40. It is one-sixth of £2.40.” The GOV.UK VAT rates page lists the rates in use: 20% standard, 5% reduced (children’s car seats and home energy, for example) and 0% for zero-rated goods such as most food and children’s clothes. The standard rate has been 20% since 4 January 2011, up from 17.5%.
| Rate | VAT fraction | VAT inside £120 | Price before VAT |
|---|---|---|---|
| 20% | 1/6 | £20.00 | £100.00 |
| 5% | 1/21 | £5.71 | £114.29 |
| 17.5% (until 2011) | 7/47 | £17.87 | £102.13 |
On this calculator the same answer comes from asking “120 is 120% of what?”: the answer, 100, is the price before VAT, and the 20 between them is the VAT.
This calculator or an answer-only one
What this page does that a typical answer-only widget does not.
| This page | A typical calculator | |
|---|---|---|
| Three question types | One box, three framings | Often three separate widgets |
| Shows the working | Every step, and a check | Usually the answer alone |
| Exact arithmetic | No floating-point drift | Floating point, sometimes 0.30000000000000004 |
| Repeating answers | 33.(3)% shown with 33.33% | Rounded without saying so |
| Fractions in | 33 1/3% accepted | Decimals only |
| Your numbers leave the browser | Never | Varies |
More calculators
Every calculator on the site runs in your browser, needs no sign-up, and sends nothing anywhere.
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Percentage increase calculator
The increase from one number to another, a number plus P%, and the original before an increase.
Open percentage increase calculator →Percentage change calculator
Percent change between two values, with percentage points and percent difference beside it.
Open percentage change calculator →Percent error calculator
Measured against accepted, signed or absolute, for one result or the mean of several trials.
Open percent error calculator →Percent to decimal
12.5% = 0.125 and 0.5% = 0.005, with the fraction, per mille and basis points.
Open percent to decimal →Decimal to percent
0.875 = 87.5%, and repeating decimals such as 0.(3) = 33.(3)% converted exactly.
Open decimal to percent →Fraction to percent
A fraction, mixed number or score such as 17 out of 20 as a percent, repeats marked.
Open fraction to percent →Percent to fraction
Any percent as a fraction in lowest terms: 37.5% = 3/8, 33 1/3% = 1/3, and why 33% is not.
Open percent to fraction →
All 18 calculators, by category: Percentages (8) · Fractions & decimals (3) · Statistics & random (1) · Health & fitness (1) · Counting & sport (5)
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 80 is 15 ÷ 100 × 80 = 0.15 × 80 = 12. For mental arithmetic, find 10% by moving the decimal point one place left, then build the rest: 10% of 80 is 8, 5% is 4, so 15% is 12.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100. 12 out of 80 is 12 ÷ 80 = 0.15, which is 15%. The whole is the number the percentage is “of”: the total, the original price or the class size. If the part is bigger than the whole, the answer is over 100%.
How do I find the whole when I know a part and its percentage?
Divide the part by the percentage written as a decimal. If 12 is 15% of something, the whole is 12 ÷ 0.15 = 80. Check it by taking 15% of 80, which gives 12 again. This is the reverse percentage, and it is how you find an original price from a deposit or a share.
What is the formula for percentage?
Part = percent ÷ 100 × whole. Rearranged, percent = part ÷ whole × 100, and whole = part ÷ (percent ÷ 100). All three everyday percentage questions are this one equation solved for a different unknown, which is why the calculator offers them together. Pick the version whose unknown you need.
Is X% of Y the same as Y% of X?
Yes. Both are X × Y ÷ 100, so 8% of 50 equals 50% of 8, which is 4. Swapping the two numbers often turns a hard mental sum into an easy one. The calculator shows the swapped form in its table for every “what is P% of” question.
How do I add or subtract a percentage from a number?
To add 15% to 80, multiply by 1.15: 92. To take 15% off, multiply by 0.85: 68. The table under the calculator shows both. Taking a percentage back off a number that already includes it is different: divide by 1.15, as the percentage increase calculator explains.
Why does my calculator show 0.30000000000000004?
Most software stores decimals in binary, where 0.1 has no exact form, so small errors appear in the last digits. This calculator keeps every number as an exact fraction of two whole numbers and only rounds the final answer, so 10% of 3 is exactly 0.3.
How is a percentage of 0 or a percentage over 100 handled?
Any percent of 0 is 0, so the calculator answers it. Asking what percent a number is of 0 has no answer and is refused with a message. Percentages over 100 are allowed: 150% of 80 is 120, and 120 is 150% of 80.
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