How to File a Self Assessment Tax Return
How to File a Self Assessment Tax Return
A practical step-by-step guide to filing your Self Assessment tax return, including what information you need, which income to declare, allowable expenses, important HMRC deadlines and how to avoid common filing mistakes.
- Updated for the 2025/26 tax year
- HMRC filing deadlines explained
- Written by ACCA qualified accountants
How Do You File a Self Assessment Tax Return?
To file a Self Assessment tax return in the UK, first make sure you are registered with HMRC, gather records of your income and allowable expenses, complete the sections of the return that apply to you, check the tax calculation and submit the return to HMRC.
For the 2025/26 tax year, which ran from 6 April 2025 to 5 April 2026, the normal deadline for filing online is 31 January 2027. Any balancing payment of tax normally due for 2025/26 is also payable by 31 January 2027.
You can file yourself using HMRC's online service where it supports your circumstances, use suitable commercial software, or appoint an accountant to prepare and submit the return for you.
What Is a Self Assessment Tax Return?
Self Assessment is HMRC's system for collecting Income Tax and certain other taxes where the correct amount has not already been collected automatically, for example through PAYE.
A tax return reports the relevant income, expenses, tax reliefs and capital gains for a tax year. HMRC then uses this information to establish your tax position, including whether additional tax is payable or whether you are due a repayment.
The UK tax year runs from 6 April to the following 5 April. The return currently being filed by most taxpayers is therefore the 2025/26 Self Assessment tax return, covering income and gains arising between 6 April 2025 and 5 April 2026.
Who Needs to File a Self Assessment Tax Return?
Whether you need to submit a return depends on your circumstances rather than simply your job title. You will normally need to file if HMRC has issued you with a notice requiring a return, and Self Assessment may also be required where you have income or gains that need to be reported.
Self-employed sole traders
You normally need to submit a return if your gross trading income was more than £1,000 during the tax year.
Business partners
Individuals who were partners in a business partnership normally need to report their share of the partnership's income through Self Assessment.
Landlords
Property income may need to be reported where you receive taxable income from renting property or land.
Investors and shareholders
A return may be required where you receive dividends, savings income or other investment income on which additional tax is due.
People with capital gains
You may need to report disposals of shares, property or other assets where Capital Gains Tax reporting requirements apply.
People with foreign income
Foreign income and gains can create UK reporting obligations, depending on your residence status and circumstances.
What Do You Need to File a Self Assessment Tax Return?
The records you need depend on your sources of income. Collecting the information before you start makes completing the return considerably easier.
| Income or claim | Typical information to gather |
|---|---|
| Personal details | UTR, National Insurance number and current contact details |
| Employment | P60, P45 and P11D or details of taxable benefits where relevant |
| Self-employment | Sales or turnover, allowable business expenses and accounting records |
| Rental property | Rental income, allowable property expenses and finance cost information |
| Dividends | Details of dividends received from UK and overseas investments |
| Savings | Bank and building society interest and other taxable savings income |
| Pensions | Taxable pension income and relevant pension contribution information |
| Capital gains | Purchase and sale proceeds, dates, acquisition costs and disposal costs |
| Foreign income | Overseas income and details of foreign tax paid where relevant |
| Tax reliefs | Eligible pension contributions, Gift Aid donations and other relevant claims |
How to File a Self Assessment Tax Return Online
The exact screens and questions depend on your circumstances, but the overall filing process can be broken down into seven stages.
Check whether you need to file
First establish whether Self Assessment applies to you. Do not assume that you need a return simply because you are a director, receive PAYE income or have a particular occupation.
If HMRC has sent you a notice requiring a tax return, you should deal with that notice even if you believe no tax is due.
Register for Self Assessment if necessary
If you need to file and are not already registered, you normally need to tell HMRC by 5 October following the end of the tax year. For 2025/26 this is 5 October 2026.
Once registered, HMRC provides a Unique Taxpayer Reference (UTR). Keep this number safe, as it identifies your Self Assessment record.
Gather your income and expense records
Collect information covering the whole tax year. This might include employment income, self-employment accounts, rental income, dividends, bank interest, pensions, foreign income and capital gains.
You should also identify expenses, allowances and tax reliefs that may legitimately reduce your taxable income or tax liability.
Choose the sections that apply to you
Self Assessment is not simply one set of questions for everyone. Different income sources can require different sections or supplementary pages.
Make sure all relevant sources of income are included. Leaving out an income source is one of the most important errors to avoid.
Enter your income, expenses and tax reliefs
Enter the figures using your underlying records. If you are self-employed, this usually includes your turnover and allowable business expenses. Landlords normally report property income and eligible property expenses.
You should also include relevant employment income, dividends, interest, pension income, capital gains and other taxable income.
Check the tax calculation carefully
Before submitting the return, review both the information entered and the resulting calculation. Check that income has not been omitted or duplicated and that expenses and reliefs have been entered correctly.
Pay particular attention to payments on account. These can make the amount payable on 31 January considerably higher than the balancing tax bill for the year just completed.
Submit the return and keep confirmation
Once you are satisfied that the return is complete, submit it electronically to HMRC. Keep a copy of the completed return, calculation and submission confirmation with your tax records.
Filing the return does not itself pay the tax. Check the amount and payment deadline shown on your Self Assessment account or calculation and arrange payment separately.
Self Assessment Deadlines for 2025/26
The 2025/26 tax year ended on 5 April 2026. For most taxpayers the important dates are:
| Self Assessment event | Normal date |
|---|---|
| 2025/26 tax year ended | 5 April 2026 |
| Return can normally be filed from | 6 April 2026 |
| Notify/register with HMRC where required | 5 October 2026 |
| Paper Self Assessment return | 31 October 2026 |
| Online Self Assessment return | 31 January 2027 |
| Balancing payment for 2025/26 | 31 January 2027 |
| First payment on account for 2026/27, if applicable | 31 January 2027 |
| Second payment on account for 2026/27, if applicable | 31 July 2027 |
Which Self Assessment Sections Do You Need?
The main individual Self Assessment return is the SA100. Depending on your circumstances, additional information or supplementary pages may also be required.
| Type of income or gain | Relevant supplementary page |
|---|---|
| Employment or company directorship | SA102 – Employment |
| Self-employment | SA103 – Self-employment |
| Partnership income | SA104 – Partnership |
| UK rental property income | SA105 – UK Property |
| Foreign income or gains | SA106 – Foreign |
| Trust or estate income | SA107 – Trusts etc. |
| Capital gains and losses | SA108 – Capital Gains Summary |
| Residence, remittance basis and certain residence matters | SA109 – Residence etc. |
Online filing software normally presents the relevant questions according to the information you provide, rather than requiring you to complete physical paper supplementary pages.
What Expenses Can You Claim on a Self Assessment Tax Return?
If you are self-employed, you can generally deduct qualifying business expenses when calculating taxable trading profit. The important test is whether the cost meets the relevant tax rules — not simply whether you paid for it from a business bank account.
| Expense category | Possible examples |
|---|---|
| Office costs | Stationery, postage and business software |
| Business premises | Rent, utilities and relevant property costs |
| Travel | Qualifying business travel and accommodation |
| Staff | Employee wages and qualifying staff costs |
| Marketing | Advertising, website and promotional expenditure |
| Professional costs | Qualifying accountancy, legal and professional fees |
| Working from home | Eligible business proportion or simplified expenses where applicable |
| Telephone and internet | The identifiable business proportion of qualifying costs |
What Are Self Assessment Payments on Account?
Payments on account are advance payments towards your next Self Assessment tax bill. Where they apply, there are normally two instalments: 31 January and 31 July.
Each payment is normally half of the relevant previous year's tax. Payments on account are generally not required where the relevant tax liability is less than £1,000 or where more than 80% of the tax was collected outside Self Assessment, for example through PAYE.
What Happens If You File Your Self Assessment Late?
If a return is required and is filed after its deadline, HMRC can charge late filing penalties. The initial late filing penalty is normally £100.
Further penalties can arise as the return becomes more overdue, including daily penalties after three months and additional penalties after six and twelve months. Separate penalties and interest can also apply to tax paid late.
If you have missed the deadline, it is generally better to deal with the outstanding return promptly rather than allowing the delay to continue.
How Long Should You Keep Self Assessment Records?
Record-retention periods depend on your circumstances. If you are self-employed, HMRC normally requires relevant business records to be kept for at least five years after the 31 January filing deadline for the relevant tax year.
For example, records supporting a 2025/26 self-employed tax return would normally need to be retained until at least 31 January 2032.
Different periods can apply to taxpayers who are not in business, late returns and cases where HMRC has opened an enquiry, so do not destroy supporting records prematurely.
Self Assessment and Making Tax Digital for Income Tax
Making Tax Digital for Income Tax has now started for some sole traders and landlords. It changes the record-keeping and reporting process for people within the rules.
| Qualifying income | MTD for Income Tax start date |
|---|---|
| More than £50,000 based on 2024/25 qualifying income | 6 April 2026 |
| More than £30,000 based on 2025/26 qualifying income | 6 April 2027 |
| More than £20,000 based on 2026/27 qualifying income | 6 April 2028 |
Qualifying income for these thresholds broadly means gross income before expenses from self-employment and property. It is not simply your taxable profit.
People within MTD for Income Tax generally need compatible software to maintain digital records, send quarterly updates and ultimately complete their tax return through the MTD process.
MTD does not mean that Self Assessment has disappeared. If you are within MTD, you still need to finalise your tax position and submit your tax return by the applicable deadline.
Common Self Assessment Mistakes to Avoid
Can an Accountant File Your Self Assessment Tax Return?
Yes. You can appoint an accountant or tax agent to prepare your Self Assessment return and submit it electronically to HMRC on your behalf.
Professional assistance can be particularly useful where you have several sources of income, self-employment, rental properties, capital gains, foreign income, significant investment income or are unsure which expenses and tax reliefs apply.
At The Online Accountants, our Self Assessment service is completed online. You provide your information and records, we prepare the return and tax calculation, send it to you for approval and then file the approved return electronically with HMRC.
How to File a Self Assessment Tax Return: FAQs
What is the deadline for the 2025/26 Self Assessment tax return?
For most taxpayers, the normal online filing deadline for the 2025/26 tax year is 31 January 2027. The normal paper return deadline is 31 October 2026.
Can I file my Self Assessment tax return before January?
Yes. You do not need to wait until January. The 2025/26 tax year ended on 5 April 2026 and the return can normally be submitted from 6 April 2026. Filing early can give you much more time to plan for the resulting tax payment.
Do I need a UTR to file a Self Assessment tax return?
If you are registered for Self Assessment, HMRC normally provides you with a Unique Taxpayer Reference, commonly called a UTR. It identifies your Self Assessment tax record.
Do company directors automatically need to file Self Assessment?
No. Being a company director does not by itself automatically require a Self Assessment return. A director may need to file because of dividends, untaxed income, capital gains or other circumstances, or because HMRC has issued a notice requiring a return.
Can an accountant submit my tax return for me?
Yes. An authorised accountant or tax agent can prepare and submit your Self Assessment return electronically to HMRC on your behalf. You should review and approve the return before it is submitted.
What happens if I make a mistake on my tax return?
Self Assessment returns can normally be amended after filing, subject to HMRC's amendment time limits. If you discover an error, deal with it promptly rather than waiting for HMRC to identify it.
Do I have to file Self Assessment if I am employed?
Not necessarily. Many employees have all of their tax collected through PAYE and do not need a return. You may still need Self Assessment if you have other taxable income, capital gains or another reason requiring a return.
What happens if I miss the Self Assessment deadline?
An initial £100 late filing penalty normally applies where a required return is filed late. Further penalties can arise after three, six and twelve months, and late payment can result in separate penalties and interest.
What are payments on account?
Payments on account are advance payments towards the following year's Self Assessment liability. Where required, they are normally paid in two instalments on 31 January and 31 July.
Can I file a Self Assessment tax return myself?
Yes. Many taxpayers file their own returns. However, the important part is not simply submitting the form: you need to identify all reportable income and gains, apply the correct expenses and reliefs and check that the resulting tax calculation is reasonable.
Let an Accountant Prepare Your Self Assessment Tax Return
If you would rather not complete your return yourself, The Online Accountants can prepare, calculate and electronically file your Self Assessment tax return with HMRC. Our service is completely online and available throughout the UK.
Reviewed for the 2025/26 Self Assessment filing cycle. Tax rules and individual circumstances vary; this guide provides general information rather than personal tax advice.