Percentages are everywhere: exam marks, sale discounts, salary raises, interest rates and tax. Yet many people still pause when asked “what is 18% of 2,450?” This guide explains how to calculate percentage in the four ways you will actually use, with simple formulas and examples. You can check every answer with our free Percentage Calculator.
What a percentage means
“Per cent” means “out of 100”. So 25% is 25 out of 100, or 0.25 as a decimal. Every percentage formula is just a way of turning a part into “out of 100” or back again.
1. Finding X% of a number
Result = number × percentage ÷ 100
Example: 18% of 2,450 = 2,450 × 18 ÷ 100 = 441.
Shortcut: 10% is the number divided by 10; 5% is half of that; 1% is the number divided by 100. So 15% of 600 is 60 + 30 = 90.
2. What percent is A of B?
Percentage = A ÷ B × 100
Example: you scored 412 out of 550. 412 ÷ 550 × 100 = 74.9%. This is the formula behind every marks percentage. Our guide on calculating marks percentage covers board and university examples.
3. Percentage increase or decrease
Change % = (new − old) ÷ old × 100
Example: a salary rises from Rs 80,000 to Rs 92,000. (92,000 − 80,000) ÷ 80,000 × 100 = 15% increase. If a price falls from 1,200 to 900, that is (900 − 1,200) ÷ 1,200 × 100 = −25%, a 25% decrease.
4. Adding or removing a percentage
To add 16% tax to Rs 5,000: 5,000 × 1.16 = Rs 5,800. To remove 16% from Rs 5,800, divide: 5,800 ÷ 1.16 = Rs 5,000. Do not subtract 16% of 5,800, because the tax was calculated on the smaller amount. The VAT Calculator does this for tax specifically.
Quick reference table
| Question | Formula |
|---|---|
| What is 20% of 350? | 350 × 0.20 = 70 |
| 45 is what % of 60? | 45 ÷ 60 × 100 = 75% |
| 50 → 65 is what change? | 15 ÷ 50 × 100 = +30% |
| 120 plus 25%? | 120 × 1.25 = 150 |
Common mistakes
- Dividing by the new value instead of the old value when finding change
- Thinking +20% then −20% returns to the start (it does not; see percentage change explained)
- Mixing percentage points and percent when comparing rates
Where you will use this
Shopping discounts (Discount Calculator), exam results, interest rates, profit margins and statistics all rely on these four formulas. Learn them once and every percentage question becomes easy.
Frequently asked questions
What is the formula for percentage?
Percentage = part ÷ whole × 100.
How do I find 15% of a number quickly?
Take 10% (divide by 10), add half of that for 5%, and add the two.
How do I calculate percentage increase?
Subtract the old value from the new, divide by the old value and multiply by 100.
How do I remove a percentage that was added?
Divide by (1 + rate). For 16%, divide by 1.16.