What is a percentage?
A percentage is a way of expressing a number as a part of one hundred. Its symbol is %, and 25% simply means "25 out of every 100" — equivalent to the fraction 25/100 or the decimal 0.25.
Percentages appear everywhere in daily life: discounts, taxes, salaries, interest rates, exam scores and financial reports. They matter because they put numbers of very different sizes on a common scale. A 50 SAR rise on a 100 SAR item and a 50 SAR rise on a 10,000 SAR item look identical in absolute terms, but as percentages they are 50% and 0.5% — an immediately obvious difference.
The core idea Every percentage problem involves three quantities: the part, the whole and the percentage. Know any two and you can always calculate the third.
How to use the percentage calculator
The calculator above is split into four tabs, each solving a different type of percentage problem. Here is how to use it:
- Pick the right tab for your question from the strip at the top of the calculator.
- Enter your two numbers in the input fields. Decimals and negative numbers are both supported, as are Arabic-Indic digits.
- Press "Calculate" or simply hit Enter on your keyboard.
- Read the result, shown in large type, with the complete formula printed underneath so you can see exactly how it was worked out.
- Check the chart — the donut visualises how large the part is relative to the whole.
- Copy the result with a single tap if you need to paste it elsewhere.
Quick tip Once a result is showing, editing either number updates the answer and the chart instantly — no need to press Calculate again.
The four percentage formulas
1. What is X% of Y?
The most common case, used for working out a discount, a tax or a commission:
Example: What is 20% of 850?
Solution: (20 ÷ 100) × 850 = 0.20 × 850 = 170.
2. X is what percent of Y?
Used to find the weight of a part within a total, such as your score as a percentage of the maximum:
Example: You scored 43 out of 50. What percentage is that?
Solution: (43 ÷ 50) × 100 = 0.86 × 100 = 86%.
3. Percentage increase or decrease
Measures change between two values relative to the original value:
Example: A price rises from 200 to 250.
Solution: ((250 − 200) ÷ 200) × 100 = (50 ÷ 200) × 100 = +25% increase.
And if the price falls from 250 back to 200:
((200 − 250) ÷ 250) × 100 = −20% decrease. Note the two percentages differ even though the absolute change is the same, because the base they are measured against changed.
4. Adding or subtracting a percentage
Useful for the final price after adding tax or applying a discount:
After subtracting = Amount − (Amount × Percent ÷ 100)
Example: A 400 item with 15% tax applied.
Solution: 400 + (400 × 15 ÷ 100) = 400 + 60 = 460.
Real-world worked examples
| Situation | Question | Calculation | Answer |
|---|---|---|---|
| Retail sale | 30% off a shirt priced 220 | 220 − (220 × 0.30) | 154 |
| VAT | Add 15% to a 640 invoice | 640 × 1.15 | 736 |
| Salary | 8% raise on 9,500 | 9,500 × 1.08 | 10,260 |
| Exam score | 38 out of 45 marks | (38 ÷ 45) × 100 | 84.44% |
| Tipping | 10% tip on a 185 bill | 185 × 0.10 | 18.50 |
| Saving | Save 20% of 7,200 income | 7,200 × 0.20 | 1,440 |
Fast mental-maths shortcuts
You do not always need a calculator. These shortcuts give you an answer in seconds:
- 10% of any number: move the decimal point one place left. 10% of 480 = 48.
- 5%: take 10% and halve it. 5% of 480 = 48 ÷ 2 = 24.
- 20%: take 10% and double it = 96.
- 1%: move the decimal two places left. 1% of 480 = 4.8.
- 15%: add 10% + 5% = 48 + 24 = 72.
- 25%: divide the number by 4 = 120.
- 50%: divide by 2 = 240.
- 75%: subtract 25% from the number = 480 − 120 = 360.
The reversal trick Percentages are commutative: X% of Y always equals Y% of X. Working out 4% of 75 looks awkward, but it equals 75% of 4 = 3, which is far easier.
Common mistakes to avoid
- Swapping the part and the whole: "15 out of 60" is 25%, not 400%. Always divide by the total.
- Adding successive percentages: 20% off followed by a further 10% off is not 30% off. Work it through: 100 → 80 → 72, a combined discount of only 28%.
- Assuming increases and decreases cancel out: a 50% rise followed by a 50% fall does not return you to the start. 100 → 150 → 75.
- Confusing percent with percentage points: a move from 5% to 7% is a rise of two percentage points, but a relative increase of 40%.
- Forgetting the base when measuring change: percentage change is always calculated against the old value, never the new one.
Converting percentages to decimals and fractions
| Percentage | Decimal | Fraction |
|---|---|---|
| 1% | 0.01 | 1/100 |
| 5% | 0.05 | 1/20 |
| 10% | 0.10 | 1/10 |
| 20% | 0.20 | 1/5 |
| 25% | 0.25 | 1/4 |
| 50% | 0.50 | 1/2 |
| 75% | 0.75 | 3/4 |
| 100% | 1.00 | 1 |
To convert a percentage to a decimal, divide by 100. To go the other way, multiply by 100.
Frequently asked questions
How do I calculate the percentage between two numbers?
Divide the part by the whole, then multiply by 100. For example, to find what percent 30 is of 120: (30 ÷ 120) × 100 = 25%. Use the second tab of the calculator above to get the answer instantly along with a chart.
What is the difference between percentage increase and decrease?
Both measure change relative to the original value, but an increase means the new value is larger and a decrease means it is smaller. The division is always by the old value, which is why going from 200 to 250 is a 25% increase while going from 250 back to 200 is a 20% decrease.
How do I work out a discount on a price?
Multiply the price by the discount percentage divided by 100 to get the saving, then subtract it from the price. A 30% discount on 220 gives a saving of 66 and a final price of 154. The "Add or subtract %" tab does this for you.
Is this percentage calculator free?
Yes, it is completely free with no sign-up and nothing to download. It runs entirely inside your browser, and every calculation happens on your own device — no data is sent to our servers.
Does the calculator work on mobile?
Yes. The site is built mobile-first, so the calculator works smoothly on phones, tablets and desktops, and it fully supports right-to-left layout in Arabic.
What are percentage points?
A percentage point is the plain arithmetic difference between two percentages. Moving from 5% to 7% is a rise of two percentage points, but it is simultaneously a relative increase of 40%, because (7 − 5) ÷ 5 = 0.40.
How do I calculate my exam score as a percentage?
Divide your score by the maximum mark and multiply by 100. Scoring 43 out of 50 gives (43 ÷ 50) × 100 = 86%. Use the second tab for this type of calculation.
Can a percentage be greater than 100%?
Absolutely. Any value larger than the reference total produces a percentage above 100%. If customers grow from 40 to 100, that is a 150% increase, and the new figure represents 250% of the original.
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