 |
| Log in to your HMRC Government Gateway account to start your tax return. |
How Do You Fill Out a Self-Assessment Tax Return in the UK?
If you are self-employed, earning a rental income, or making extra money from a side hustle, you will likely need to send a Self-Assessment tax return to HM Revenue and Customs (HMRC).
Filling out your tax return can feel daunting, but the online system splits the process into manageable steps. Here is a clear, step-by-step guide on how to complete and submit your Self-Assessment accurately to avoid any late penalties.
Before diving into the paperwork, make sure you are legally required to file.
You can check our quick guide on how to know if you need to register for Self Assessment first.
1. Register for Self-Assessment
Before you can fill out any forms, you must register with HMRC to get a Unique Taxpayer Reference (UTR) number.
The Deadline: You must register by 5 October in the second tax year of your business or extra income.
Activation Code: Once registered, HMRC will post an activation code to set up your personal Government Gateway online account.
2. Gather Your Financial Records
Do not log into the system until you have all your paperwork organized. Having these documents next to you will save you time:
Your UTR and Government Gateway login details.
P60 and P45 forms (if you also worked an ordinary employment job during that tax year).
Records of all business income (invoices, sales receipts, and bank statements).
Receipts for allowable business expenses (such as stock, travel costs, or office utilities).
Certificates for other income, including bank interest, dividend payouts, or rental property income.
3. Fill Out the Form Online
Log into the official GOV.UK website using your Government Gateway user ID. The online form adapts dynamically based on your answers.
Step A: Welcome and Personal Details
Confirm your name, date of birth, home address, and telephone number. Ensure your National Insurance number is correct.
Step B: Tailor Your Return
The software will ask a series of simple 'Yes' or 'No' questions (e.g., "Were you self-employed?", "Did you receive income from property?"). Your answers here dictate exactly which extra sections open up next, filtering out forms you do not need.
Step C: Enter Income and Expenses
Go through each active section and type in your precise financial totals.
Turnover: Enter the gross amount of money your business brought in before any deductions.
Allowable Expenses: Enter your legitimate business expenses. If your turnover is under £85,000, you can usually just enter one single total figure for expenses rather than itemizing them.
Step D: Claim Tax Reliefs
Fill out sections regarding pension contributions, donations to charities via Gift Aid, or marriage allowances. These details can lower your overall tax bill.
4. Review, View Calculation, and Submit
Before hitting the final button, the system gives you a chance to double-check your data.
Check for Errors: Review your typed numbers against your paper bank statements.
View Your Calculation: Click the "View your calculation" link. The website will instantly show you exactly how much tax and National Insurance you owe, or if you are owed a refund.
Submit: Agree to the legal declaration and submit the digital form. Keep a record of your submission receipt number.
5. Pay What You Owe
Submitting the form is only half the job. You must pay the money you owe to HMRC by the strict deadlines:
The Deadline: Both the online form submission and the final payment must clear by 31 January following the end of the tax year.
Payments on Account: If your tax bill is more than £1,000, you may also have to pay an extra advance payment toward your next year's tax bill on 31 January and 31 July.