UK Self Assessment for freelancers: the SA103 self-employment pages

If you work for yourself as a sole trader in the UK, your self-employment income goes on the self-employment pages (SA103S short or SA103F full) of your Self Assessment tax return. Here's who has to file, how to register, which pages to use, the expense boxes as printed on the forms, the trading allowance, working from home, deadlines and penalties, records, and how it ties to National Insurance and payments on account.

Checked against GOV.UK guidance and HMRC's SA103S / SA103F forms and notes on 2026-10-13. The forms online then were the 2026 editions, for the tax year 6 April 2025 to 5 April 2026 (2025–26). Not written by a tax professional.

The short answer

• You must send a tax return if, in the last tax year (6 April to 5 April), you were self-employed as a sole trader and earned more than £1,000 before taking off anything you can claim tax relief on (Who must send a tax return).
• The self-employment pages go with the main SA100 return: SA103S if your turnover was below £90,000 and your business is straightforward, SA103F otherwise (Self-employment (short) notes 2026).
• Expenses go in labelled boxes (SA103S boxes 11–19, or just a total in box 20). Claim only the business part. Or use the £1,000 trading allowance instead of expenses — not both (Expenses if you're self-employed; Trading allowance).
• For 2025 to 2026: paper return by 31 October 2026, online return and payment by 31 January 2027 (Deadlines).
• Keep records for at least 5 years after the 31 January submission deadline for that tax year (How long to keep your records).

1. Who has to send a tax return

Self Assessment is how HMRC collects Income Tax on income that isn't taxed automatically, like self-employment profits. You fill in the return after the end of the tax year it applies to, and you must send one if HMRC asks you to (Self Assessment tax returns).

• As a sole trader you must send a return if you earned more than £1,000 in the last tax year, before taking off anything you can claim tax relief on. Partners in a business partnership must also send one (Who must send a tax return).
• You can start trading straight away without registering, but you must register for Self Assessment as a sole trader if you earn more than £1,000 in a tax year (Set up as a sole trader).
• You can also choose to send a return, for example to prove you're self-employed or to pay voluntary National Insurance (Who must send a tax return).
• If you're not sure, GOV.UK has a check if you need to send a tax return tool.

2. Registering and the 5 October date

You must tell HMRC by 5 October 2026 if you need to complete a return for 2025 to 2026 and you have either not sent a return before, or registered before but didn't need to send one for the year before. You tell HMRC by registering for Self Assessment, and you get a Unique Taxpayer Reference (UTR) (Register for Self Assessment).

• If you register after 5 October 2026, HMRC sends a letter or email with a different filing deadline, 3 months from the date on it — but you must still pay the tax you owe by 31 January 2027 (Deadlines).
• Registering late and not paying all of your bill by 31 January can bring a ‘failure to notify’ penalty, based on the amount still left to pay (Penalties).

3. SA103S or SA103F?

The self-employment pages are supplementary pages of the SA100 return (SA100 tax return; Sending a return). The 2026 short notes say (SA103S notes):

• SA103S (short): if your turnover was less than £90,000 (or would have been if you'd traded for a full year) (SA103S publication page).
• SA103F (full): if your turnover was £90,000 or more, your business is more complicated, your accounting period needs adjusting (for example it wasn't 12 months long), or you have adjustment income from changing accounting basis, among other cases (SA103S notes; SA103F publication page).
• Use separate self-employment pages for each business. Don't send receipts, accounts or paperwork with the return unless HMRC asks for them (SA103S notes).

4. Income and the trading allowance

On SA103S, box 9 is your turnover — the takings, fees, sales or money earned by your business before expenses — including all payments (cash, card, cheque or any other method) and tips, fees and commissions. Box 10 is any other business income. On SA103F turnover is box 15 (SA103S 2026 form; notes; SA103F 2026 form).

• Trading allowance: up to £1,000 a year of tax-free trading income. If your gross trading income is more than that, you can deduct the allowance instead of your actual expenses and other allowances (Tax-free allowances on property and trading income).
• On SA103S it goes in box 10.1. If you claim it, don't fill in the expense boxes, and you can't use it to make a loss (SA103S notes).

5. Expense boxes on the forms

You can deduct allowable business expenses to work out your taxable profit. You can only claim the business part of something you also use privately, and money you take out for personal use isn't an expense (Expenses if you're self-employed). The short notes say the cost of entertaining, depreciation of equipment, your own salary or drawings, and your National Insurance are not allowable expenses (SA103S notes).

SA103S 2026: boxes 11 to 19

If your turnover was below £90,000, you may just put your total expenses in box 20 rather than filling in each box (SA103S 2026).

SA103F 2026: boxes 17 to 30

The full pages have more boxes, a total in box 31, and a second column for any disallowable part you included (SA103F 2026).

Whether a particular cost is allowable, and how much, depends on HMRC's rules for that kind of cost — these tables are only the forms' labels. Box 21 (net profit) or 22 (net loss) on SA103S comes after the total (SA103S 2026).

6. Working from home and simplified expenses

If you work from home you may be able to claim a proportion of costs such as heating, electricity, Council Tax, mortgage interest or rent, and internet and phone use. Use a reasonable way of dividing the costs, such as the number of rooms you use for business or the time you spend working there (Expenses if you're self-employed).

• Simplified expenses are optional flat rates for some vehicles, working from home and living at your business premises; all other expenses are worked out from actual costs (Simplified expenses).
• The working-from-home flat rate needs 25 hours or more of business use a month and doesn't include phone or internet (claim those at actual cost) (Working from home flat rates):

Vehicle costs: our free UK mileage log records business journeys and works out HMRC's mileage rates if you use the flat-rate route for a vehicle.

7. Cash basis, traditional accounting and capital allowances

• From the 2024 to 2025 tax year, cash basis is the default: you record income and expenses when money comes in or goes out. You must opt out if you want to use traditional accounting (Business records if you're self-employed; Cash basis).
• On SA103S, put an ‘X’ in box 8 if you used traditional accounting instead of cash basis (SA103S 2026).
• With traditional accounting you claim capital allowances for equipment, machinery and business vehicles instead of including them as expenses. With cash basis, only cars go through capital allowances; other items you buy and keep for the business are claimed as allowable expenses. Neither is available if you use the trading allowance (Expenses if you're self-employed; SA103S notes).

8. Profit, National Insurance and payments on account

• Your taxable profit from the business ends up in box 31 on SA103S. HMRC works out what you owe from what you report (SA103S 2026; Self Assessment tax returns).
• Class 2: if your total profits for 2025 to 2026 are less than £6,845 you don't have to pay Class 2, but you can choose to pay voluntarily (box 36) to protect your State Pension and certain benefits. At £6,845 or more, contributions are treated as paid (SA103S notes).
• Class 4 National Insurance is part of your Self Assessment bill and of any payments on account (Payments on account); box 37 is only for people who are exempt (SA103S notes). Our free UK self-employed National Insurance calculator walks through Class 4 and Class 2 with the GOV.UK rates.
• Payments on account: you may have to pay towards next year's bill in two halves by 31 January and 31 July, unless last year's bill was under £1,000 or more than 80% was already deducted at source (Payments on account). Our free payments on account checker covers it in detail.

9. Deadlines and penalties

For the 2025 to 2026 tax year (6 April 2025 to 5 April 2026) GOV.UK gives these dates; the return and payment deadlines are 11:59pm on the day (Self Assessment deadlines):

• 5 October 2026: register for Self Assessment, if you need to.
• 31 October 2026: paper tax return.
• 30 December 2026: online return, if you want the bill collected through your tax code.
• 31 January 2027: online tax return, and paying the tax you owe (31 January 2027).

• Late filing: an initial £100 penalty; after 3 months, £10 a day up to £900; after 6 and again after 12 months, 5% of the tax due or £300, whichever is greater (Penalties).
• Late payment: 5% of the tax unpaid at 30 days, 6 months, 12 months, plus interest (Penalties).
• If you don't know your full-year profit by the deadline, you can file provisional figures, tell HMRC, and amend within 12 months of the deadline (Sending a return).

10. Records and Making Tax Digital

• Keep records of your business income and expenses for your return, plus records of your personal income. It can be easier if your records run to the tax year (6 April to 5 April) (Business records if you're self-employed).
• Keep them for at least 5 years after the 31 January submission deadline of the relevant tax year — HMRC may check them (How long to keep your records).
• Making Tax Digital for Income Tax: sole traders with qualifying income over £50,000 for 2024 to 2025 should have started using it from 6 April 2026; over £30,000 for 2025 to 2026 means from 6 April 2027; over £20,000 for 2026 to 2027 means from 6 April 2028. You still send a Self Assessment return for the tax year before you start (Making Tax Digital for Income Tax).

Keeping those records

Free tools on this site that fit Self Assessment habits (they run in your browser; nothing is sent or saved):

• Free invoice generator and free receipt generator — invoices in pounds (with a VAT line if you're registered) and receipts for payments, as PDFs.
• Free timesheet — a record of the hours you work, handy if you use the working-from-home flat rate (it's based on hours).
• UK mileage log — business journeys and HMRC mileage rates.
• UK self-employed National Insurance calculator, payments on account checker and VAT registration threshold checker.

For a running spreadsheet of invoices, payments and expenses that can follow the SA103F expense boxes (with yearly totals by category and a UK payments-on-account tab), our paid Freelance Billing Kit by Small Rows (US$12, one-time) is built for freelancers who bill in any currency. It doesn't file your return or suggest a tax rate.

Where the sources differ

We read the pages under Sources on 2026-10-13. A few details to watch:

• Short vs full is not only about turnover. The GOV.UK publication pages describe SA103S as for turnover below the VAT threshold; the notes give the £90,000 figure and also send you to SA103F for more complicated businesses or accounting periods that need adjusting. Read the notes for the year you file.
• The two forms group expenses differently. SA103S has 9 expense boxes (interest and bank charges together; “other allowable business expenses”, with client entertaining not allowable). SA103F has 14 (separate loan interest and bank charges, “advertising and business entertainment costs”, with a disallowable column). Box numbers on this page are from the paper PDFs; if you file online, go by the labels.
• Old “last updated” dates, current wording. Several GOV.UK guides show an old page date (the records guide's is 2015, the deadlines guide's 2024), yet their text already has the 2024 to 2025 cash-basis change and the 31 January 2027 deadline. We go by the wording on the day we checked.
• The 5 October date had passed. On 2026-10-13 the 5 October 2026 registration date for 2025 to 2026 was already behind us. GOV.UK says late registrants get a filing deadline 3 months from HMRC's letter, but the 31 January 2027 payment date still applies.

When to talk to a tax adviser

• you're not sure whether you're self-employed, employed, or both;
• your accounting period doesn't line up with the tax year, or you're changing accounting basis;
• you have losses to use, capital allowances on a vehicle, staff, or stock;
• you live in Scotland or Wales and have questions about income tax bands, or you have income from abroad;
• you've had an HMRC letter about Making Tax Digital, a penalty or a compliance check.

Related free resources

• UK Self Assessment payments on account — who has to make them, the 31 January and 31 July amounts, with a checker.
• UK self-employed National Insurance calculator — Class 4 and Class 2 on your profits.
• UK VAT registration threshold checker — your rolling 12-month turnover against the threshold.
• What a UK VAT invoice must show and the UK late payment interest calculator.
• UK mileage log and HMRC mileage rates calculator.
• Schedule C for US freelancers and Form T2125 for Canadian freelancers, if you also file there.
• All free tools.

Sources

GOV.UK guidance and HMRC forms and notes, read on 2026-10-13. Check the live page before you rely on it.

• Self Assessment: Self Assessment tax returns · Who must send a tax return · Register for Self Assessment · Set up as a sole trader · Sending a return · Deadlines · Penalties
• Forms: SA100 tax return · SA103S publication · SA103S 2026 PDF · SA103S notes 2026 PDF · SA103F publication · SA103F 2026 PDF · SA103F notes 2026 PDF
• Expenses and records: Expenses if you're self-employed · Trading and property allowances · Simplified expenses · Working from home flat rates · Cash basis · Business records · How long to keep records
• Paying: Payments on account · Making Tax Digital for Income Tax

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