Guides / How to file a Self Assessment tax return
Guide
How to file a Self Assessment tax return
A step-by-step guide to filing your Self Assessment return online: what to gather first, which pages to complete, how to check your figures and how to pay.
8 min read · Updated October 2026 · Reviewed by qualified accountants
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In short
- Register with HMRC and get your UTR and online account set up before you start.
- Gather your income and expense records for the whole tax year, 6 April to 5 April.
- Complete the pages that match your income, then check the tax calculation before you submit.
- File by 31 January and pay your bill by the same date.
- You can amend a submitted return within 12 months of the filing deadline.
What you need before you start
Filing is much quicker when everything is in one place. You will need:
- your Unique Taxpayer Reference (UTR) and National Insurance number
- your Government Gateway user ID and password
- income records: sales invoices, bank statements, rent statements, P60 or P45 forms and statements of interest or dividends
- expense records for any business or property costs you plan to claim
- details of pension contributions, Gift Aid donations and any student loan or Child Benefit position
If you have never filed before, register first. See our guide to Self Assessment deadlines for the dates.
Step-by-step: filing your return online
- Sign in to your HMRC online account with your Government Gateway details and open your Self Assessment account.
- Start the return for the correct tax year and answer the questions that decide which pages you need.
- Enter your income from each source: employment, self-employment, rent, savings, dividends and anything else.
- Claim your expenses and reliefs, such as business costs, pension contributions and Gift Aid.
- Review the tax calculation HMRC produces. Check that every number matches your records.
- Submit and save your confirmation. Keep the receipt and a copy of your figures.
- Pay any tax due by 31 January, using your UTR as the payment reference.
Tip
Save your return as you go. The online service lets you come back and finish later, so you do not need to do it all in one sitting.
Which pages of the return do you need?
The main return, the SA100, is always required. You then add supplementary pages for the types of income you have:
| Page | Use it for |
|---|---|
| SA102 | Employment income and benefits |
| SA103 | Self-employment |
| SA105 | UK property income |
| SA106 | Foreign income |
| SA108 | Capital gains |
The online service shows only the pages that apply to you once you answer its questions, so you do not need to download forms yourself.
Common mistakes to avoid
- Mixing up turnover and profit. You pay tax on profit after allowable expenses, not on total income.
- Leaving out small amounts of income, such as interest or one-off earnings. HMRC already holds a lot of this data.
- Claiming personal costs as business expenses.
- Forgetting reliefs you are entitled to, like Gift Aid and pension contributions.
- Not keeping records for the required time.
Paying your tax
Your tax is due by 31 January after the tax year ends. You can pay online by debit card, by bank transfer, or by setting up a Direct Debit. Always use your UTR as the payment reference. If you cannot pay in full, contact HMRC early to ask about a Time to Pay arrangement, because interest and penalties for late payment apply from the due date.
After you have filed
HMRC checks your return and may contact you if something looks wrong. If you spot an error after submitting, you can amend your return online within 12 months of the 31 January filing deadline. Keep your records for at least five years after the 31 January deadline if you are self-employed or let property, and at least 22 months after the end of the tax year otherwise.
When to use an accountant
Filing online is possible for simple affairs, but many people choose help when they have several income sources, rental properties, a limited company, capital gains, or they simply want to be sure the return is right. We prepare and file Self Assessment returns for a fixed fee from £199 + VAT, confirmed in writing before we start.
Get a fixed price
Tell us about your income and we confirm your fee before any work begins.
Written and reviewed by the Accotax tax team
Accotax is a London firm of qualified accountants and tax consultants, on the ICAEW approved employers list. Our team prepares Self Assessment, landlord and company tax returns every day, and each guide is checked against GOV.UK before it is published and updated every tax year.
Related
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Authorised and regulated
Is Cheap Tax Returns authorised and regulated? Yes.
Your return is prepared by qualified UK accountants holding qualifications from the leading accountancy bodies: ICAEW, ACCA and AAT. We are also on the ICAEW approved employers list, so you can file with confidence.
Regulated by the professional bodies. Reviewed by qualified accountants. Part of Accotax.
Prepared by accountants you can trust.
Questions, answered.
HMRC normally posts your UTR within 10 working days, or 21 days if you live abroad. Start early.
Yes. Our accountants prepare and file the return, and you approve it before it is sent.
With organised records, a simple return can take under an hour. Returns with several income sources or lots of expenses take longer, which is why many people use an accountant.
You can use the HMRC online service on a phone, but a computer makes it easier to enter figures and check the calculation.
You can amend the return online within 12 months of the 31 January filing deadline. After that you need to write to HMRC to correct it.
Not for the standard online return. You can file through HMRC’s free online service. Commercial software or an accountant can make it faster.
Next steps
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Know your price before we start.
- Fixed fee confirmed in writing before any work begins
- ICAEW, ACCA and AAT-qualified accountants
- Filed with HMRC and confirmed, so you have proof
- A real person on the phone: 0203 4411 258