Everyday calculations
Percentage Calculator
This percentage calculator answers the five questions people actually ask: what is X% of Y, X is what percent of Y, X is Y% of what, and how to increase or decrease a number by a percentage.
Pick the question that matches yours, fill in the two boxes, and the answer appears with a plain-English sentence you can check it against.
Calculator
Fill in the boxes above and your answer appears here.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
What is 15% of 200?
- 15% of 200
- 30
15% of 200 is 30.
30 is what percent of 120?
- Percentage
- 25%
30 is 25% of 120.
Increase 250 by 8%
- New amount
- 270
- Difference
- 20
250 increased by 8% is 270.
The formulas
- X% of Y = Y × X ÷ 100. So 15% of 200 = 200 × 15 ÷ 100 = 30.
- X is what percent of Y = X ÷ Y × 100. So 30 is 30 ÷ 120 × 100 = 25% of 120.
- X is P% of what = X ÷ (P ÷ 100). So 20 is 25% of 20 ÷ 0.25 = 80.
- Increase by P% = Y × (1 + P ÷ 100). 250 increased by 8% = 250 × 1.08 = 270.
- Decrease by P% = Y × (1 − P ÷ 100). 80 decreased by 25% = 80 × 0.75 = 60.
Quick mental shortcuts
10% of anything is the number divided by 10, and 1% is the number divided by 100. Build other percentages from those: 15% is 10% plus half of it, 5% is half of 10%, and 30% is three lots of 10%. To find 15% of 80, take 8 (that's 10%) and add 4 (that's 5%) to get 12.
Percentages and percentage points
If an interest rate goes from 4% to 5%, it has risen by 1 percentage point, but by 25 percent (1 ÷ 4). The two phrases mean different things, so be careful which one you're reading. For the percentage change between two values, use the percentage change calculator.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. 15% of 200 is 200 × 15 ÷ 100 = 30. Or turn the percentage into a decimal (0.15) and multiply.
How do I find what percentage one number is of another?
Divide the part by the whole and multiply by 100. 30 out of 120 is 30 ÷ 120 = 0.25, which is 25%.
How do I increase a number by a percentage?
Multiply it by 1 plus the percentage as a decimal. To increase 250 by 8%, multiply by 1.08 to get 270.
How do I find the original number if I only know a percentage of it?
Divide the part by the percentage as a decimal. If 20 is 25% of a number, divide 20 by 0.25 to get 80.
Can a percentage be more than 100%?
Yes. 150% of 40 is 60. Percentages over 100% mean the amount is bigger than the whole you compared it to.
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Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.