Hi Lyndsey Longden
You can either claim the £1000 trading allowance or expenses, but not both.
You will declare your gross turnover, your expenses or claim the trading income allowance of £1000. What's left is then your net profit and is taxable.
Please take a look at a paper SA103S, which can be downloaded at
Self Assessment: self-employment (short) (SA103S) and the notes that go with it.
Please also have a look at
HS222 How to calculate your taxable profits (2024), which advises how to calculate your taxable profits.
Thank you