SA103S explained box by box (2025/26)

Updated 21 October 2026 · For the 2025/26 tax year (return due 31 January 2027)

The SA103S is the short self-employment section of your Self Assessment return. HMRC says to use it if you're self-employed, have relatively simple affairs and your annual turnover was below the VAT threshold – £90,000 – for the tax year. That covers almost every side hustle. This guide follows the 2025/26 form (for the tax year ended 5 April 2026, filed by 31 January 2027). If you file online you won't see the paper form, but the online questions map to these boxes.

Business details: boxes 1–8

• Box 1 – Description of business: keep it plain, e.g. "Handmade candles sold online" or "Freelance graphic design".
• Box 2 – Postcode of your business address: usually your home postcode for a side hustle.
• Box 3: tick if your business name, description, address or postcode changed in the last 12 months.
• Box 4: tick if you're a foster carer or shared lives carer (special rules apply).
• Box 5Q and 5: did the business start after 5 April 2025? If yes, enter the start date.
• Box 6Q and 6: did the business stop before 6 April 2026? If yes, enter the final trading date.
• Box 7 – Date your books are made up to: for most people simply 5 April 2026 (anything from 31 March to 5 April is accepted).
• Box 8: tick only if you used traditional (accruals) accounting rather than the cash basis. Since 2024/25 the cash basis is the default, so most side hustles leave this blank.

Business income: boxes 9–10.1

• Box 9 – Turnover: all your takings, fees and sales for the year before deducting any costs or platform fees. For an Etsy or eBay seller, include postage you charged buyers.
• Box 10 – Any other business income: things not included in box 9, such as grants or rebates relating to the business.
• Box 10.1 – Trading income allowance: if you choose the £1,000 trading allowance instead of claiming expenses, enter it here (up to £1,000, but not more than your income). If you use box 10.1, you can't claim expenses in boxes 11–20.

Allowable expenses: boxes 11–20

If your turnover was below £90,000 you may just put your total expenses in box 20. If you itemise, the boxes are:

Box	What goes in it
11	Cost of goods bought for resale or goods used – stock, materials, supplies
12	Car, van and travel expenses – e.g. 45p a mile simplified mileage for business journeys
13	Wages, salaries and other staff costs
14	Rent, rates, power and insurance costs – including the use-of-home flat rate
15	Repairs and maintenance of property and equipment
16	Accountancy, legal and other professional fees
17	Interest and bank and credit card financial charges – e.g. payment processing fees
18	Phone, fax, stationery and other office costs – including postage and packaging
19	Other allowable business expenses – e.g. advertising, platform fees, software. Client entertaining isn't allowable.
20	Total allowable expenses – the total of boxes 11 to 19

Net profit or loss: boxes 21–22

Box 21 is net profit: box 9 + box 10 minus box 20, if positive. Box 22 is net loss if expenses were higher. If you used the trading allowance in box 10.1, skip these and go to box 28.

Capital allowances: boxes 23–26

Under the cash basis most equipment is simply an expense, so side hustles rarely need these. Box 23 is the Annual Investment Allowance, 24 the small pool allowance, 24.1 the zero-emission car allowance, 25 other capital allowances, 25.1 and 25.2 structures and buildings allowances, and 26 balancing charges (for example when you sell an asset you claimed on).

Taxable profit: boxes 27–32

• Box 27 – Goods and/or services for your own use: the value of stock you took for yourself.
• Box 28 – Net business profit for tax purposes: box 21 + 26 + 27 minus boxes 22–25.2. If you used box 10.1, it's box 9 + box 10 + box 27 minus box 10.1 (the form words this as box 21 + 26 + 27 minus 10.1).
• Box 29: losses brought forward from earlier years.
• Box 30: any other business income not in box 9 or 10.
• Box 31 – Total taxable profits from this business; box 32 is a net loss for tax purposes.

Losses: boxes 33–35

If you made a tax loss, these let you set it against other income this year (33), carry it back (34) or carry it forward (35). Read the SA103S notes – loss relief has restrictions.

National Insurance and CIS: boxes 36–38

• Box 36: if your total profits for 2025/26 are less than £6,845 and you choose to pay Class 2 NI voluntarily (to protect benefits like the State Pension), put X here. Above £6,845 you don't pay Class 2 but get the NI credit anyway.
• Box 37: tick if you're exempt from Class 4 NI (e.g. over State Pension age at the start of the year).
• Box 38: Construction Industry Scheme deductions – not relevant to most side hustles.

Class 4 NI itself is calculated by HMRC from your profits: 6% between £12,570 and £50,270, and 2% above.

Frequently asked questions

Who should use the SA103S short form?

Self-employed people with relatively simple affairs and annual turnover below the VAT threshold (£90,000) for the tax year. Most side hustles qualify.

What is box 10.1 on SA103S?

Box 10.1 is the trading income allowance. Enter up to £1,000 here (not more than your income) if you're using the allowance instead of claiming expenses. If you use it, leave the expense boxes 11 to 20 blank.

Do I have to fill in every expense box?

No. If your turnover was below £90,000 you can put total expenses in box 20 instead of itemising boxes 11 to 19.

Do I need a paper SA103S if I file online?

No. Online, HMRC asks the same questions on the self-employment pages in a slightly different order; the box numbers help you match up your figures.

Sources (GOV.UK, checked 21 October 2026)

• Self Assessment: self-employment (short) (SA103S)
• Tax-free allowances on property and trading income
• Self-employed National Insurance rates
• Simplified expenses if you're self-employed
• Expenses if you're self-employed

General information, not tax advice. Rules can change – always check GOV.UK or speak to an accountant. January Sorted is not affiliated with HMRC.

More side hustle tax guides

• Self Assessment deadline 31 January 2027: what to file and pay
• Do I need to tell HMRC about my side hustle?
• Etsy seller tax UK: what to declare for 2025/26
• Trading allowance vs expenses: which saves you more tax?