A percentage is a part out of 100
15% means 15 out of every 100, whether the 100 is marks, rupees or people. Every formula on this page is that one idea, rearranged — divide by 100 to get the decimal, multiply by 100 to get the percent.
Free percentage calculator
Percentage Calculator
Pick the question, enter two numbers, and get the answer with the working shown — whether it is a discount, exam marks, a salary hike or a price change.
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12
15% of 80
4 modes
Percent of, percent, change, after
Instant
Working shown
Everyday maths, not financial advice. This tool is for discounts, marks, salary hikes and price changes. It is not financial, tax or legal advice; for tax, GST or loan figures, check with a qualified adviser.
Calculate a percentage
15% of 80Example figures are filled in. Replace them with your own numbers.
YOUR ANSWER
WORKING SHOWN BELOW
Your answer
12
15% OF 80
0.15
AS A DECIMAL
80
THE WHOLE (100%)
Your answer at a glance
15% of 80 is 12.
15 ÷ 100 = 0.15.
0.15 × 80 = 12.
A percentage is a part out of 100 — 15% means 15 out of every 100.
Results are shown to two decimal places; the full figure is used until the final rounding, so the working above always reproduces the answer.
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Understand the result
What does a percentage calculator do?
A percentage is a part out of 100 — 15% means 15 out of every 100. The same four questions come up again and again: what is X% of a number, what percent is one number of another, how much did a number change by, and what does a number become after a percent rise or fall. This calculator answers all four, with the working shown, so you can check every number instead of trusting a black box.
The base decides the answer
The same percent means a different amount on a different base: 15% of 80 is 12, but 15% of 2,000 is 300. Most percentage mistakes are base mistakes — dividing by the new value instead of the old one, or adding percentages from different bases.
Four questions cover almost everything
Almost every percentage question is one of four: X% of a number, X as a percentage of Y, the change from one number to another, or a number after a rise or fall. Pick the mode that matches your question and the calculator does the rest.
How it works
From two numbers to an answer
Pick the question first — the labels change to match it — then enter two numbers and read the answer with the working.
Pick the question
Four modes cover almost every percentage question: X% of a number, X as a percentage of Y, the percentage change from one number to another, and a number after a percentage rise or fall.
Enter the two numbers
Plain numbers only — no % signs, commas or currency symbols. The labels change to match the mode you picked.
Read the answer with the working
The result appears as you type, with the step-by-step working underneath so you can check every number.
Try a preset, or check the table
Load a real-life example — a discount, exam marks, a salary hike — or look the figure up in the common-percentages table.
The calculation, explained
The four percentage formulas
Four formulas, one idea: a percentage is a fraction out of 100. X% of Y = (X ÷ 100) × Y. X as a percentage of Y = (X ÷ Y) × 100. Percentage change from A to B = (B − A) ÷ |A| × 100. A number after a percentage change = Y × (1 ± X ÷ 100). Results are shown to two decimal places; the full figure is used until the final rounding.
1. Turn the percent into a decimal
15 ÷ 100 = 0.15
Divide the percentage by 100.
2. Multiply by the number
0.15 × 80 = 12
Multiply the decimal by the number.
3. Read the answer
15% of 80 = 12
The result is shown to two decimal places.
Percentage points are not the same as percent
If a rate rises from 20% to 25%, that is a rise of 5 percentage points — but a 25% relative increase (5 ÷ 20 × 100). Mixing the two up is the most common percentage mistake in news reports and exam answers alike.
Worked examples
Four questions, four answers
One example for each mode. Select any example to load it into the calculator and check the working for yourself.
15% of 80 is 12
15 ÷ 100 = 0.15, and 0.15 × 80 = 12. So 15% of 80 is 12 — the same working a shopkeeper uses for a 15% discount.
15% of 80 = 12
450 out of 600 is 75%
450 ÷ 600 = 0.75, and 0.75 × 100 = 75%. So 450 marks out of 600 is 75% — divide the marks scored by the total, then multiply by 100.
450 is 75% of 600
₹50,000 to ₹55,000 is a 10% rise
55,000 − 50,000 = 5,000, and 5,000 ÷ 50,000 × 100 = 10%. So a salary moving from ₹50,000 to ₹55,000 rose by 10%.
50,000 → 55,000 = +10% (increase)
15% off ₹2,000 leaves ₹1,700
15% of 2,000 is 300, so the sale price is 2,000 − 300 = 1,700. That is the discount taken off, then subtracted from the original price.
2,000 decreased by 15% = 1,700
Common percentages at a glance
Common percentages at a glance
What each common percentage works out to on four round numbers — the figures people look up most.
| Percentage | of 100 | of 500 | of 1,000 | of 5,000 |
|---|---|---|---|---|
| 5% | 5 | 25 | 50 | 250 |
| 10% | 10 | 50 | 100 | 500 |
| 15% | 15 | 75 | 150 | 750 |
| 20% | 20 | 100 | 200 | 1,000 |
| 25% | 25 | 125 | 250 | 1,250 |
| 50% | 50 | 250 | 500 | 2,500 |
| 75% | 75 | 375 | 750 | 3,750 |
| 90% | 90 | 450 | 900 | 4,500 |
The table shows why the base matters: 25% is 25 on a base of 100, but 1,250 on a base of 5,000. Always check which number the percentage is taken from before trusting an answer.
Common mistakes
Four ways to get a percentage wrong
The formulas are short, but four readings trip people up. Each one can turn a right method into a wrong answer.
Adding percentages from different bases
A 10% rise followed by a 10% fall is not back to the start — it is 99% of the original, a net fall of 1%. Each percentage applies to the new value, so changes are multiplied, never added.
Confusing percentage points with percent
A rate rising from 20% to 25% is up 5 percentage points, but the relative rise is 25%. Saying "up 25%" and "up 5 points" describe the same move in different units — pick the right one.
Dividing by the wrong number
Percentage change divides by the old value, and "X as a percent of Y" divides by Y. Dividing by the new value instead gives a different, wrong answer — 50 on 200 is 25%, not 20%.
Rounding in the middle of the working
Rounding 0.15 × 80 is harmless, but rounding a decimal like 1 ÷ 3 to 0.33 before multiplying turns 33.33% into 33%. Keep the full figure until the final answer, as this calculator does.
Your questions, answered
Percentage calculator FAQs
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For 15% of 80: 15 ÷ 100 = 0.15, and 0.15 × 80 = 12. The same method works for money: 18% GST on ₹5,000 is 0.18 × 5,000 = ₹900.
How do I work out what percentage one number is of another?
Divide the first number by the second and multiply by 100. For 450 marks out of 600: 450 ÷ 600 = 0.75, and 0.75 × 100 = 75%. That is how exam percentages are calculated in India — obtained marks divided by total marks, times 100.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100. A price rising from ₹200 to ₹250 is (250 − 200) ÷ 200 × 100 = 25%. If the result is negative, the value fell — a price dropping from ₹250 to ₹200 is a 20% decrease.
What is the difference between percentage change and percentage points?
Percentage points measure the gap between two percentages; percentage change measures that gap against the starting value. A rate rising from 20% to 25% is a rise of 5 percentage points, but a 25% relative increase (5 ÷ 20 × 100). News reports usually mean percentage points when they say 'up 5 points'.
How do I find the original price after a discount?
Divide the sale price by (1 − discount ÷ 100). A jacket selling for ₹1,700 after 15% off cost 1,700 ÷ 0.85 = ₹2,000 before the discount. The same trick works for a price after a rise: divide by (1 + rise ÷ 100).
How do I calculate a discount price?
Work out the discount first, then subtract it. At 15% off ₹2,000 the discount is 15 ÷ 100 × 2,000 = ₹300, so you pay 2,000 − 300 = ₹1,700. Or use the 'after a change' mode on this page — decrease ₹2,000 by 15%.
How do I calculate my exam percentage from marks?
Divide the marks you scored by the total marks and multiply by 100. Scoring 450 out of 600 gives 450 ÷ 600 × 100 = 75%. If subjects carry different maximum marks, add all your marks and all the maximums first, then divide the two totals.
Why is a 10% rise followed by a 10% fall not back to the start?
Because the second percentage is taken from a different base. Start at 100: a 10% rise gives 110, and a 10% fall from 110 takes off 11, leaving 99 — a net fall of 1%. Percentage changes are never added together; each one applies to the new value.
Does this calculator send my numbers anywhere?
No. Every calculation runs entirely on this page — nothing is sent to a server, nothing is stored, and reloading the page clears your recent checks.
About the method
This page uses the four standard percentage formulas: X% of Y = (X ÷ 100) × Y; X as a percentage of Y = (X ÷ Y) × 100; percentage change from A to B = (B − A) ÷ |A| × 100; and a number after a percentage change = Y × (1 ± X ÷ 100). Results are shown to two decimal places, and the full figure is used until the final rounding, so the working you see always reproduces the answer shown. A "what percent" or "change" question needs a non-zero base — dividing by zero has no answer, so the calculator says so instead of guessing.
Cross-checked 11 November 2026 against the ranking percentage calculators: 15% of 80 is 12 on calcsolver.in, which shows the same working (15 ÷ 100 = 0.15; 0.15 × 80 = 12), and 450 out of 600 is 75% on realbill.in, which uses the same marks example. The formulas are standard arithmetic; no rule on this page comes from a competitor.
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