What is X% of Y?
The classic percentage calculation: take a percentage of any number. Numbers below default to 20% of 150 = 30; change them to your own.
To find a percentage of a number, divide the percentage by 100 and multiply by the number. The calculator above does it instantly. Below: worked UK examples, the formula, and the most common questions about it.
How it works.
Formula: (X ÷ 100) × Y.
How to work out a percentage of a number, step by step:
- Divide the percentage by 100 (so 20% becomes 0.20).
- Multiply the result by your number.
Worked example — 20% of 150: 20 ÷ 100 = 0.20; 0.20 × 150 = 30.
Mental-maths shortcut. 10% of any number is the number with the decimal moved one place left (10% of 350 = 35). Then double, halve, or add to get other percentages: 20% = double 10%; 5% = half of 10%; 15% = 10% plus half of 10%.
Worked examples
20% of £150 = £30 — e.g. a 20% deposit on a £150 phone case.
5% of £35,000 = £1,750 — a typical UK pay rise on a median graduate salary.
20% of £1,200 = £240 — the VAT on a £1,200 net invoice (UK standard rate).
40% of £80,000 = £32,000 — the higher-rate income tax on the slice of salary above £50,270 (illustrative, before personal allowance).
0.5% of £450,000 = £2,250 — an estate agent's fee at the cheaper end of UK pricing.
Sources:
HMRC Income Tax rates and allowances · HMRC VAT rates
· retrieved 2026-05-13.
Frequently asked questions
How do you work out a percentage of a number?
Divide the percentage by 100, then multiply by the number. 20% of 150: 20 ÷ 100 = 0.20; 0.20 × 150 = 30. 5% of 35,000: 5 ÷ 100 = 0.05; 0.05 × 35,000 = 1,750. The same formula works for any pair of numbers.
What is the formula for X% of Y?
Multiply the two: (X ÷ 100) × Y. So 20% of 150 = (20 ÷ 100) × 150 = 0.2 × 150 = 30.
How do I work out a percentage in my head?
Use 10% as the anchor. 10% of any number is the number with the decimal moved one place left. Then double, halve, or add to get other percentages: 20% is double 10%; 5% is half of 10%; 15% is 10% plus half of 10%.
How do I calculate VAT-inclusive prices?
For UK standard-rate VAT (20%), multiply the net price by 1.20 to get gross. To remove VAT from a gross price, divide by 1.20. The reverse-percentage calculator on this site does that directly.
Does this calculator round?
Results display to 4 decimal places. Internally the maths is exact — rounding is for display only. Currency calculations on UK sites typically round to 2 decimal places (pence).
What if my number is bigger than 100%?
The same formula works. 150% of 200 is (150 ÷ 100) × 200 = 300. Percentages above 100 just mean «more than the whole».