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Your first self-assessment tax return, step by step (for sole traders)

The first one is the hardest, mostly because you don't know what it will ask. Here's what to have ready, what goes where, and what happens once you press send.

Stephen Evans, editor
Figures checked against GOV.UK and HMRC guidance
Last checked 29 Oct 2026 · Next review Apr 2027

The short answer

Tax year 2026/27

To send your first self-assessment return you need your Unique Taxpayer Reference, sign-in details for HMRC online services and a record of your income and costs for the tax year, 6 April to 5 April. For a sole trader the main part is the self-employment section: your turnover, your allowable expenses or the £1,000 trading allowance, and any CIS tax deducted. You can send it from 6 April after the tax year ends, and it's due online by 31 January 2027, along with any tax you owe. You don't have to do it in one go: the online return saves as you work.

Before you start

  • Your UTR. The 10-digit Unique Taxpayer Reference HMRC posted to you when you registered. If you haven't registered yet, do that first: see how to register as self-employed.
  • Sign-in details. If you don't have any, you can create them the first time you sign in. You may be asked to prove your identity, usually with photo ID such as a passport or driving licence.
  • Your records for the tax year. What came in and what went out between 6 April and 5 April, with the receipts and bank statements behind them.

If you registered in an earlier year but haven't sent a return for a while, you may need to reactivate your account before you file, or the return can be delayed.

The figures you'll need

  • Turnover. Everything customers paid you in the tax year, including what you charged for materials. Most sole traders use the cash basis, which has been the standard method since the 2024/25 tax year: count money when it arrives, not when you send the invoice.
  • Expenses. Your allowable business costs, such as van running costs, tools, materials, insurance and your phone. Our guide to tradesman expenses goes through what counts. You can claim the £1,000 trading allowance instead, but not both; for most trades the real costs are bigger.
  • CIS deductions. If you work under the Construction Industry Scheme, add up the tax on your monthly payment and deduction statements. It counts towards your bill, and often means money back: see claiming a CIS refund.
  • Other income. Pay and tax from a job (your P60 has both), savings interest and any rent.
  • Your student loan plan, if you have one, because repayments on self-employed income are collected through the return.

Short or full self-employment pages

If your turnover was under the VAT registration threshold, £90,000, and your affairs are simple, you fill in the short version of the self-employment pages. That's most tradespeople in their first year. Online, you don't pick a form: your answers about your income decide which sections you see.

Filing it online, step by step

  1. Sign in. Use file your Self Assessment tax return online on GOV.UK, with your UTR to hand.
  2. Choose the right year. The return due by 31 January 2027 is for 2025/26: the tax year that ended on 5 April before it.
  3. Say what income you had. Self-employment, a job, interest and so on. This sets which sections you fill in.
  4. Fill in the self-employment section. Your business details, turnover, expenses or the trading allowance, and any CIS tax deducted.
  5. Add the rest. Other income, and your student loan plan if you have one.
  6. Check the figures and submit. You can save and come back at any point before this. Once it's sent, the calculation shows the tax you owe.

The paper return is still an option, but its deadline is three months earlier: 31 October 2026 for this year's return.

After you send it

  • Pay by 31 January 2027. If your bill is over £1,000, HMRC usually also asks for half of it again towards next year, due the same day. That's why the first January is the expensive one: see payments on account.
  • Can't pay it all? Ask for a payment plan before the bill is overdue.
  • Need proof of income? You can print your tax calculation 72 hours after you file: see getting your SA302.
  • Spotted a mistake? You can correct the return online for 12 months after the deadline. Wait 72 hours after filing first.
  • Keep your records for at least 5 years after the 31 January deadline.

If you registered late

If you told HMRC after 5 October 2026 that you need to send a return, HMRC gives you a later deadline for the return: 3 months from the date on its letter or email. The tax is still due by 31 January 2027. Our late penalty calculator shows what happens if either is late.

If you'd rather hand it over

An accountant or an online tax return service can do it for you from your figures. You still need the records above, and it's still your responsibility if it's late, so send them your figures well before January.

Common questions

Do I need an accountant for my first return?

No. Most sole traders with simple affairs can do it online themselves. An accountant or a tax return service makes sense if your affairs are complicated or you'd rather hand it over, but book early: January is their busiest month.

What if I don't know my exact figures?

Use your best estimate, called provisional figures, say so when you submit, and change the return once you have the real numbers. You have 12 months from the deadline to change it. If the real figures mean more tax, interest is charged from the original payment date.

I made a loss. Do I still send it?

Yes, if you're registered and HMRC expects a return. The return records the loss, which you may be able to set against other income or carry forward.

How long do I keep my records?

At least 5 years after the 31 January deadline for that return. Records for a return due in January 2027 need keeping until at least the end of January 2032.

Can I change it after I've sent it?

Yes, within 12 months of the deadline. Wait 72 hours after filing, then sign in, choose the tax year, make the corrections and file it again.

Related toolCheck the tax on your profit before you file

Sources

  1. File your Self Assessment tax return online, GOV.UK. Checked 29 Oct 2026
  2. Self Assessment tax returns: sending a return, GOV.UK. Checked 29 Oct 2026
  3. Self Assessment tax returns: deadlines, GOV.UK. Checked 29 Oct 2026
  4. Self Assessment tax returns: if you need to change your return, GOV.UK. Checked 29 Oct 2026
  5. Business records if you're self-employed, GOV.UK. Checked 29 Oct 2026
  6. Self Assessment: self-employment (short) (SA103S), GOV.UK. Checked 29 Oct 2026
  7. Tax-free allowances on property and trading income, GOV.UK. Checked 29 Oct 2026

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