Self Assessment Tax Return: A Practical Guide for UK Taxpayers
If you earn money that is not fully taxed through PAYE you may need to fill out a Self Assessment Tax Return and send your income details to HM Revenue & Customs (HMRC). Knowing who has to file, how to sign up and when to pay can help you keep your tax duties straight and dodge fines.
What Is a Self Assessment Tax Return?
A Self Assessment Tax Return is a form you use to tell HMRC about your earnings and other money matters. Depending on your situation you may also have to add expenses, tax breaks and other important data.
Self Assessment is usually used by people who run their business sole traders, business partners, landlords and anyone who has some other kind of taxable income.
Tax is normally taken straight from your salary through PAYE. If some of your tax is left out you may have to report that money through Self Assessment.
The UK tax year starts on 6 April. Ends on 5 April next year. HMRC uses the details you give in your Self Assessment Tax Return to calculate how tax you owe.
Who Must File a Self Assessment Tax Return?
Not everyone has to fill out a Self Assessment Tax Return. Whether you need to sign up and file depends on your situation.
You might have to file if you:
Are self-employed or run a sole-trader business
Are a partner in a business partnership
Get rental or property income
Get certain dividend or savings income
Have income, from abroad
Need to report Capital Gains Tax or another taxable event
If you are not sure if a Self Assessment Tax Return is needed you should look at HMRCs Self Assessment guidance.
How Does Self Assessment Work?
The process can be split into a clear steps:
Check → Register → Keep Records → Complete Your Return → Submit → Pay
If this is your first time you may need to register with HMRC. Once you are registered HMRC will give you a Unique Taxpayer Reference (UTR).
You then must keep records of your income and related expenses during the tax year. When the year ends those records are used to fill out your Self Assessment Tax Return.
After you send your return HMRC works out your tax bill based on what you told them.
How to Register for Self Assessment
If you need to file a Self Assessment Tax Return for the time you may have to sign up with HMRC.
1. Check Whether You Need to Register
Begin by seeing if your income or circumstances mean that a Self Assessment registration is required.
2. Register with HMRC
Fill in the registration form through HMRC.
If you were registered before but did not need to send a return that year you might have to reactivate your Self Assessment account of opening a new one.
3. Receive Your UTR Number
Once you are registered HMRC will issue the Unique Taxpayer Reference (UTR). This is usually a 10-digit number that you use for all Self Assessment matters.
4. Set Up Your Online Account
Follow HMRCs directions to open your account and manage your Self Assessment.
5. Keep Your UTR Safe
Your UTR is a reference so store it safely. You will need it when you send your Self Assessment Tax Return or talk to HMRC.
For the 2025–26 tax year if you have never filed before and need a Self Assessment Tax Return you normally have to let HMRC know by 5 October 2026.
How Long Does Self Assessment Registration Take?
Getting your UTR can take a while because HMRC must process your registration.
So it is best to sign up instead of waiting for the deadline. Filing early also lets you see how tax you owe and gives you more time to pay.
Lost Your UTR?
If you have already signed up for Self Assessment but cannot find your UTR you usually do not need to register
You can look at your HMRC account or past HMRC letters. If you still cannot find it call HMRC for help.
How to Complete Your Self Assessment Tax Return Online
Once you are registered you can fill out your Self Assessment Tax Return online through your HMRC account. Having your money records ready first will make the job smoother.
Step 1: Gather Your Records
Before you start collect the stuff you may need like:
Employment income and PAYE information
Self-employed income and invoices
Business expenses
Bank interest and dividends
Rental income and allowable expenses
Pension contributions
Details of taxable income
Keep relevant records such as invoices, receipts and bank statements so that you can support the information included in the Self Assessment Tax Return if required.
A practical approach is to keep income and expenses updated throughout the year of trying to collect everything just before the deadline.
Step 2: Log In to Your HMRC Account
Sign in to your HMRC account and open the Self Assessment service.
Make sure you are completing the Self Assessment Tax Return for the tax year.
Step 3: Check Your Personal Details
Review your information and make sure the details shown on your account are correct.
Step 4: Enter Your Income
Enter the income that applies to your circumstances for the tax year.
Depending on your situation this may include:
Employment income
income
Rental income
Savings and interest
Dividends
Foreign income
Other taxable income
Make sure you report all relevant income and enter the figures for the correct tax year.
Step 5: Enter Your Expenses
If you are entitled to claim allowable expenses enter the relevant amounts in the appropriate sections of the Self Assessment Tax Return.
Keep supporting records as HMRC may ask you to provide evidence.
Step 6: Add Tax Reliefs and Other Information
Complete any sections that apply to you such as pension contributions, tax reliefs, Capital Gains Tax or other relevant information.
Only complete the sections that apply to your circumstances.
Step 7: Review Your Self Assessment Tax Return
Before submitting the Self Assessment Tax Return check all the information you have entered.
Pay attention to:
Income figures
Expense claims
Tax reliefs
Personal details
The tax year
Additional sources of income
A final review can help identify simple errors before you submit the Self Assessment Tax Return.
Step 8: Submit Your Self Assessment Tax Return
Once you are satisfied that the information is correct submit the Self Assessment Tax Return online.
HMRC will calculate your tax liability based on the information provided.
Step 9: Check Your Tax Bill
After submitting the Self Assessment Tax Return check your tax calculation amount due and payment deadline.
Some taxpayers may also need to make payments on account towards their tax bill.
Self Assessment Tax Return Deadlines
For the 2025–26 tax year, which runs from 6 April 2025 to 5 April 2026 the main deadlines are:
5 October 2026 – deadline to tell HMRC if you need to file a return for the tax year and have not filed one before
31 October 2026 – deadline for paper tax returns
31 January 2027 – deadline for online tax returns
31 January 2027 – deadline to pay the tax owed
31 July 2027 – second payment on account, where applicable
Different deadlines can apply in certain circumstances so always check the relevant HMRC guidance for your situation.
What Are Payments on Account?
Payments on account are advance payments towards the Self Assessment tax bill.
Where applicable they are generally made in two instalments:
31 January
31 July
Each payment is normally half of the years relevant tax liability. Payments on account do not apply to everyone.
This is particularly important for people filing Self Assessment for the time because, where payments on account apply the January payment can include both the tax due for the year just filed and the first payment towards the following years bill.
Keeping Accurate Records
Good record-keeping is a part of Self Assessment.
Depending on your circumstances you may need to keep records of:
Sales and income
Invoices and receipts
Business expenses
Bank statements
income
Interest and dividends
Pension contributions
Other relevant financial information
Keeping these records organised throughout the year makes it easier to prepare the Self Assessment Tax Return and provide supporting evidence if HMRC asks for it.
For taxpayers HMRC generally requires business records to be kept for at least 5 years after the 31 January submission deadline, for the relevant tax year.
Common Self Assessment Mistakes and How to Avoid Them
straightforward tax returns can contain mistakes. Common examples include:
Forgetting to report income
Entering incorrect figures
Claiming expenses that’re not allowable
Using the wrong tax year
Forgetting savings or dividend income
Missing income
Failing to keep proper financial records
Submitting the return after the deadline
Forgetting to pay the tax after submitting the return
The best way to avoid these issues is to keep your records organised all year and to carefully review your Self Assessment return before you submit it.
What Happens If You Pay Your Tax Late?
If you do not pay your Self Assessment tax by the required deadline HMRC can charge interest. Impose late payment penalties.
The consequences depend on factors like how late the payment’s how much money is still owed.
If you are having difficulty paying your tax bill do not simply ignore it. HMRC gives options for people who cannot pay in full, such as payment arrangements when conditions are met.
Frequently Asked Questions
What is a UTR number?
A UTR (Unique Taxpayer Reference) is a reference number that HMRC gives you when you register for Self Assessment. It is normally a 10-digit number.
Do I need to file a Self Assessment Tax Return every year?
If you continue to meet the requirements for Self Assessment you will normally need to submit a return for every tax year in which you must report your income.
What is the UK tax year?
The UK tax year runs from 6 April to 5 April of the year.
What is the Self Assessment deadline?
For taxpayers who file online the deadline is 31 January after the end of the relevant tax year. For the 2025–26 tax year the online filing deadline is 31 January 2027.
What are payments on account?
Payments on account are advance payments that go toward your Self Assessment tax bill. Where they apply they are usually paid in two instalments on 31 January and 31 July.
Can I submit my tax return early?
Yes. You do not have to wait until the deadline. Once the relevant tax year has ended and you have the needed information you can submit your Self Assessment return
Can I correct a mistake after submitting my tax return?
In cases you can amend your Self Assessment return after you submit it as long as you follow HMRC rules and the relevant time limits.
Final Thoughts
Completing a Self Assessment return does not have to be difficult. The key is to understand your reporting responsibilities keep records and stay aware of the relevant deadlines.
Whether you are self-employed a landlord, a business partner or you have another source of income following the process step by step can make filing your Self Assessment return much easier.
Tax rules and deadlines can change, so always check the HMRC guidance for the relevant tax year or seek professional tax advice if you are unsure, about your circumstances.
