How do I calculate a percentage of a number?

To find X% of Y, multiply Y by X and divide by 100. Example: 15% of £280 = 280 × 15 ÷ 100 = £42. Equivalently, multiply by the decimal: 280 × 0.15 = 42.

How do I calculate percentage change?

Percentage change = ((New value − Old value) ÷ Old value) × 100. If a salary rises from £35,000 to £37,450, the change is ((37,450 − 35,000) ÷ 35,000) × 100 = 7.0%. A negative result means a decrease.

How do I add VAT to a price?

To add 20% VAT, multiply the net price by 1.20. Example: £850 × 1.20 = £1,020 (gross including VAT). To find just the VAT amount: £850 × 0.20 = £170. Alternatively, use our VAT calculator for a full breakdown of net, VAT and gross amounts.

How do I work out a percentage tip?

Multiply the bill by the tip percentage divided by 100. Example: 15% tip on a £65 bill = £65 × 0.15 = £9.75. A common UK custom is to tip 10–15% in restaurants. Some establishments include a service charge — check the bill before tipping.

Percentage Calculator UK | % Of, % Change, Increase & Decrease

How Percentages Work — Quick Reference

What is X% of Y?

Multiply Y by X ÷ 100. Example: 15% of £280 = 280 × 0.15 = £42. Useful for: VAT amounts, discounts, commission, tips, pension contributions.

X is what % of Y?

Divide X by Y and multiply by 100. Example: £42 of £280 = (42 ÷ 280) × 100 = 15%. Useful for: finding what proportion one number is of another — your tax rate, your savings rate, the deposit percentage on a house.

Percentage change

((New − Old) ÷ Old) × 100. Example: salary rising from £35,000 to £37,450 = ((37,450 − 35,000) ÷ 35,000) × 100 = 7%. A negative result means a decrease. Useful for: pay rises, investment returns, inflation comparisons.

Percentage increase / decrease

Increase: multiply by (1 + rate/100). Decrease: multiply by (1 − rate/100). Example: £45,000 increased by 5.5% = £45,000 × 1.055 = £47,475. A 20% discount on £65 = £65 × 0.80 = £52.

Common UK percentage shortcuts

20% VAT: Multiply by 1.2 to add VAT. Divide by 1.2 (or multiply by 5 ÷ 6) to remove it.
5% VAT: Multiply by 1.05 to add. Divide by 1.05 to remove. VAT is 1/21 of the gross price.
10% tip: Divide by 10. A 15% tip: find 10%, then add half again.
Tax bands: Basic rate = 20% on income between £12,570 and £50,270. Higher = 40% above £50,270.

Worked Examples

VAT calculation

Net invoice£850

VAT rate20%

20% of £850£170

Gross (inc. VAT)£1,020

Salary pay rise

Current salary£45,000

Pay rise5.5%

Increase£2,475

New salary£47,475

Retail discount

Original price£65

Discount20%

Saving£13

Sale price£52

Frequently Asked Questions

Multiply the number by the percentage divided by 100. Example: 15% of £280 = 280 × (15÷100) = 280 × 0.15 = £42. Equivalently: 10% of £280 is £28 (divide by 10), so 15% = £28 + £14 = £42.

Percentage change = ((New − Old) ÷ Old) × 100. If a salary rises from £35,000 to £37,450: ((37,450 − 35,000) ÷ 35,000) × 100 = (2,450 ÷ 35,000) × 100 = 7.0%. A negative result indicates a decrease. This formula works for any quantity — prices, investments, populations.

To add 20% VAT: multiply by 1.20. Example: £850 × 1.20 = £1,020. To remove 20% VAT from a gross price: divide by 1.20. Example: £1,020 ÷ 1.20 = £850. For 5% VAT: multiply by 1.05 to add, divide by 1.05 to remove. The VAT element in a 5% gross price is always 1/21 of the gross.

Multiply the bill by the tip percentage ÷ 100. Example: 15% on a £65 bill = £65 × 0.15 = £9.75. Quick mental method: 10% of £65 = £6.50; 5% = £3.25; 15% = £6.50 + £3.25 = £9.75. Some UK restaurants include a discretionary 12.5% service charge — always check the bill before adding a further tip.

Related Calculators

How percentage calculations work in everyday UK finance

Percentages are foundational to UK financial calculations — from interest rates to tax bands, from VAT to mortgage deposits, from inflation to investment returns. Understanding the four core percentage operations covers nearly all everyday needs: percentage OF a number ("what is 20% of £150?" → £30), one number AS a percentage of another ("what percentage is £30 of £150?" → 20%), increase/decrease BY a percentage ("£150 increased by 20%" → £180), and reverse-percentage ("what was the original price before 20% VAT?" → £150 / 1.20 = £125).

The most common UK financial percentage applications: VAT calculations (20% standard rate, 5% reduced rate, 0% zero rate) — to ADD VAT to a £100 net price, multiply by 1.20 (£120); to STRIP VAT from a £120 gross price, divide by 1.20 (£100). Income tax bracket math — 20% basic, 40% higher, 45% additional rates applied to specific income slices. Mortgage Loan-to-Value (LTV) calculation — £200,000 mortgage on a £250,000 property = 80% LTV. Compound interest projections — £10,000 at 5%/year for 10 years = £10,000 × (1.05)^10 = £16,289.

Practical UK examples requiring percentage math: pay rise calculations ("a 4% pay rise on £30,000 = £1,200 extra/year, but real-terms loss if inflation is 5%"); pension contribution sizing ("5% workplace pension on £40,000 = £2,000/year gross"); SDLT band calculations ("5% on the £75,000 between £250,000 and £325,000 = £3,750"); credit-card APR understanding (a 22% APR on a £1,000 balance carried for a year = £220 of interest, compound monthly = slightly more). Even savings: a 4.5% AER on £20,000 means £900/year if interest is taken annually, or slightly more with monthly compounding.

Common percentage pitfalls: "100% increase" doubles a number, "200% increase" triples it (the increase IS the multiplier, not the result). A 50% decrease followed by a 50% increase doesn't restore the original — £100 falling 50% to £50 then rising 50% reaches only £75. Percentage differences vs percentage point differences matter: tax rising from 20% to 22% is a 2 percentage-point increase but a 10% relative increase. These distinctions matter for mortgage rates, pension projections, and financial reporting.