Verified answer

Sales £24000 - costs £3000 = £21000 profit.

Assuming no other income, £21000 profit minus personal tax allowance £8105 = £12895 taxable income; at 20% = £2579 income tax, plus National Insurance Contributions of course.

Free calculator on gov.uk and in the tax return software.

Firstly you do not pay tax on what you earn. You pay tax on your profit which is earnings less expenses.

Without knowing your tax code we cannot say how much tax you pay.

Google "uk income tax" and sites pop up that do the sums for you.

As you lack very basic knowledge of finance it would benefit you to make an appointment with an accountant. He can advise you of all expenses that would reduce your tax bill. His fee is one of them.

My accountant saved me more money than I paid him.