Quick answer: to find X% of a number, divide X by 100 and multiply: 15% of 240 = 0.15 × 240 = 36. To find what percent A is of B, divide and multiply by 100: 45 ÷ 60 × 100 = 75%. For a percentage change, divide the difference by the old value: from 80 to 100 is 20 ÷ 80 = +25%.
The three formulas behind every percentage question
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | Y × X ÷ 100 | 15% of 240 = 36 |
| X is what % of Y? | X ÷ Y × 100 | 45 of 60 = 75% |
| Percentage change from A to B | (B − A) ÷ A × 100 | 80 → 100 = +25% |
| Increase Y by X% | Y × (1 + X ÷ 100) | 1,200 + 18% = 1,416 |
| Decrease Y by X% | Y × (1 − X ÷ 100) | 1,200 − 18% = 984 |
Why up 25% and down 20% are the same move
A percentage change is always measured against the starting value. Going from 80 to 100 is +25% (20 out of 80), but coming back from 100 to 80 is −20% (20 out of 100). That’s why a price that drops 50% has to rise 100% to recover, and why a 10% pay cut followed by a 10% rise still leaves you 1% short.
Percentage points vs. percent
If an interest rate goes from 4% to 5%, it has risen by 1 percentage point – but by 25 percent (1 is a quarter of 4). News reports mix these up all the time. Use percentage points when you subtract two percentages, and percent when you compare them.
Quick mental tricks
- 10%: move the decimal point one place left (10% of 340 = 34). 5% is half of that, 20% is double.
- X% of Y = Y% of X: 8% of 50 is the same as 50% of 8 = 4.
- Reverse VAT or GST: don’t subtract the rate – divide by (1 + rate). Use the sales tax calculator.
For shopping, the discount calculator handles stacked offers; for business pricing, the profit margin calculator explains the difference between margin and markup. Students converting a CGPA can use the CGPA to percentage calculator.
How to calculate a percentage
- Choose the question. Pick “X% of a number”, “X is what % of Y”, “% change” or “Add / subtract %”.
- Type the two numbers. Decimals and negative numbers work. The result appears as you type.
- Read the working. Below the answer you see the exact formula with your numbers filled in.
- Copy the result. Tap Copy result to paste the answer and working into a message or spreadsheet.
Worked example: a price drop
A jacket was 1,800 and is now 1,350. What is the percentage decrease?
- Difference: 1,350 − 1,800 = −450.
- Divide by the old price: −450 ÷ 1,800 = −0.25.
- Multiply by 100: −25%, a 25% decrease.
Check it the other way: 1,800 × (1 − 0.25) = 1,350. ✓
Common percentage mistakes
- Dividing by the new value. 450 ÷ 1,350 = 33% is the increase needed to get back up, not the decrease.
- Adding percentages with different bases. +10% then −10% is −1%, not 0%.
- Confusing percent and percentage points. 4% → 5% is +1 point but +25%.
- Removing tax by subtracting the rate. Divide by 1.18 instead of taking 18% off.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 240 is 240 × 15 ÷ 100 = 36.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100. 45 out of 60 is 45 ÷ 60 × 100 = 75%.
How do I calculate percentage increase?
Subtract the old value from the new one, divide by the old value and multiply by 100. From 80 to 100: (100 − 80) ÷ 80 × 100 = 25%.
What is the difference between percentage change and percentage difference?
Percentage change compares to the starting value. Percentage difference compares to the average of both values and has no direction; this calculator shows both.
Can a percentage be more than 100%?
Yes. 150 is 150% of 100, and a price that goes from 50 to 200 has increased by 300%.
How do I add 18% to a price?
Multiply by 1.18. 1,200 × 1.18 = 1,416. To take 18% off, multiply by 0.82.
How do I find the original price before a percentage increase?
Divide by (1 + rate). If 1,416 includes an 18% increase, the original is 1,416 ÷ 1.18 = 1,200.
How do I calculate a percentage of a total in Excel?
Divide the part by the total and format the cell as a percentage: =A2/B2. For X% of a number, use =B2*15%.
What is 20% of 500?
100. Multiply 500 by 20 and divide by 100, or move the decimal for 10% (50) and double it.