Navigating the world of Self Assessment tax returns can feel daunting, especially if you’re new to self-employment, letting property, or have other forms of untaxed income. But don’t worry, you’re not alone! Each year, millions of people across the UK successfully file their returns with HMRC. For expert support navigating this process, explore our Self Assessment services.
This comprehensive guide is designed to walk you through the entire process for the 2024/25 tax year (covering income earned between 6 April 2024 and 5 April 2025). We’ll cover everything from registering and gathering documents to filling out the forms and meeting the crucial tax deadlines. Whether you’re a seasoned filer needing a refresher or tackling your first tax return, this guide provides clear, actionable steps.
What is Self Assessment?
Self Assessment is the system HMRC (His Majesty’s Revenue and Customs) uses to collect Income Tax. If you receive income that hasn’t been taxed at source through PAYE (Pay As You Earn), you’ll likely need to declare it by completing a Self Assessment tax return. This includes profits from self-employment, income from rental income, certain investment profits like Capital Gains Tax, and more. Essentially, it’s your way of telling HMRC about your earnings and calculating how much tax you owe. You can find more details on general accounts and tax services here.
Who Needs to File a Self Assessment Tax Return?
You generally need to send a tax return if, in the last tax year (6 April to 5 April), any of the following applied:
- Self-Employment: You were self-employed as a ‘sole trader’ and earned more than £1,000 (before taking off anything you can claim tax relief on – this is your ‘trading allowance’).
- Partnership: You were a partner in a business partnership.
- Rental Income: You received £2,500 or more from renting out property. (Check if you can use the Rent a Room Scheme for income up to £7,500). Specific guidance on property accounts is available.
- Savings & Investments: You had significant income from savings or investments (e.g., £10,000 or more before tax).
- Dividends: You earned significant income from dividends.
- Capital Gains Tax: You made profits from selling chargeable assets (like shares or a second home) and need to pay Capital Gains Tax.
- Company Director: You were a company director (unless it was for a non-profit and you didn’t get pay or benefits). See our company secretarial work services.
- High Income: Your income (or your partner’s) was over £50,000, and one of you claimed Child Benefit.
- State Pension: Your State Pension was more than your Personal Allowance and was your only source of income (unless you started getting it after 5 April 2016).
- Foreign Income: You had untaxed income from overseas that is liable for UK tax (check Self Assessment for Foreign Income rules).
- PAYE Underpayments: HMRC has notified you that you owe tax from a previous year that couldn’t be collected through your tax code.
- Claiming Expenses: You need to claim expenses or reliefs worth over £2,500.
- Side Hustles: You earned over £1,000 from a ‘side hustle’ or casual work. Consider our advice for small businesses.
- Crypto Assets: You made gains from selling crypto assets which are subject to Capital Gains Tax.
Important Update for 2024/25: From the 2024/25 tax year onwards, the requirement for employees or pensioners with income over £150,000 taxed entirely via PAYE to file a Self Assessment return has been removed. You only need to file if one of the other criteria applies.
If you’re unsure, use the HMRC tool to check if you need to send a Self Assessment tax return or contact us for advice.
Key Self Assessment Tax Deadlines UK
Missing deadlines can lead to Self Assessment tax penalties, so it’s crucial to be aware of these key dates for the 2024/25 tax year. You can also check our Tax Calendar 2024-25 for a full overview.
| Deadline | Task | Notes |
|---|---|---|
| 5 October 2025 | Register for Self Assessment | If you’re filing for the first time for the 2024/25 tax year. |
| 31 October 2025 | Submit Paper Tax Return | Midnight deadline. Less common now, online is preferred. |
| 30 December 2025 | Submit Online Return (if you want HMRC to collect tax via PAYE code) | Only if you owe less than £3,000 and meet other criteria. |
| 31 January 2026 | Submit Online Tax Return | Midnight deadline for online submission. |
| 31 January 2026 | Pay Your Tax Bill | Deadline for paying the tax owed for 2024/25 AND the first Payment on Account. |
| 31 July 2026 | Pay Second Payment on Account | If applicable, for the 2025/26 tax year. |
Always aim to file well before the deadline to avoid last-minute stress and potential technical issues.
Step-by-Step Guide to Filling in Your Tax Return
Let’s break down the process into manageable steps:
Step 1: Register for Self Assessment
If you haven’t filed before, you need to register. The process differs slightly depending on your circumstances:
- Self-Employed/Sole Trader: Register online via the GOV.UK website. You’ll need your National Insurance number. We can assist with business start-ups and registrations.
- Not Self-Employed (e.g., Rental Income, Capital Gains): You’ll need to fill in form SA1. You can do this online or print and post it. Register for Self Assessment via GOV.UK.
- Partnership: The nominated partner registers the partnership. Individual partners also need to register separately.
What happens next? HMRC will send you a Unique Taxpayer Reference (UTR) number, usually within 10 working days (21 if you’re abroad). Keep this safe! You’ll also need to set up your Government Gateway account to access the HMRC Self Assessment login for online filing.
Action: If you need to file for 2024/25 and haven’t registered before, do it before the 5 October 2025 deadline.
Step 2: Gather Your Documents and Information
Preparation is key to a smooth filing process. Collect all relevant financial records for the tax year (6 April 2024 – 5 April 2025):
- UTR Number: Essential for identifying yourself to HMRC.
- National Insurance Number.
- Income Records:
- P60 form (if employed) showing income and tax paid.
- P45 form (if you left a job during the tax year).
- P11D or P9D form detailing benefits and expenses (if employed).
- Invoices issued (if self-employed).
- Records of rental income received (if a landlord). See our property accounts service.
- Dividend vouchers or statements.
- Interest statements from banks and building societies.
- Details of any foreign income.
- Records of Capital Gains (purchase/sale details of assets).
- Pension statements (State Pension and private pensions).
- Details of any other untaxed income (e.g., from side hustles, crypto asset sales).
- Expense Records:
- Receipts and invoices for allowable business expenses (e.g., office costs, travel, stock, professional fees for Self Assessment for Sole Traders).
- Records of expenses related to rental income (e.g., repairs, letting agent fees, insurance).
- Details of pension contributions made.
- Records of charitable donations eligible for Gift Aid (Self Assessment Tax Relief). Consider personal tax planning to maximise reliefs.
- Other Relevant Information:
- Details for claiming reliefs like the Marriage Allowance.
Tip: Keep organised digital or paper records throughout the year. Cloud accounting solutions can make gathering information much easier.
Step 3: Choose How to File (Online Recommended)
While paper returns are an option (deadline 31 October), filing online via the HMRC portal is generally faster, easier, and gives you until 31 January.
- Online Filing: Use your Government Gateway ID and password to access the HMRC Self Assessment login. The online system guides you through the sections relevant to your circumstances and performs calculations automatically.
- Paper Filing: Download the main Self Assessment Tax Return Form (SA100) and any relevant supplementary pages from GOV.UK. Fill them in by hand and post them to HMRC by 31 October.
- Accountant/Tax Advisor: You can authorise an accountant to file on your behalf. See how Ask Accountants UK Ltd can help.
- Commercial Software: You can use HMRC-recognised software to file your return.
Recommendation: File online for convenience, automatic calculations, and the later deadline.
Step 4: Filling in the Tax Return (SA100 and Supplementary Pages)
The main tax return form is the SA100. Depending on your income sources, you may also need to complete supplementary pages. The online system automatically includes the sections you need based on your initial answers.
- SA100 (Main Tax Return): Covers income from employment, pensions, benefits, interest, and dividends (up to certain limits), plus charitable donations and your Personal Allowance.
- SA103 (Self-Employment): For sole traders and self-employed individuals. You’ll report your turnover, allowable business expenses, and calculate your profit or loss. There are short (SA103S) and full (SA103F) versions depending on your turnover.
- SA105 (UK Property): For reporting rental income and expenses from UK properties. Our property accounts experts can assist with this.
- SA106 (Foreign): For reporting foreign income or gains.
- SA108 (Capital Gains Summary): For reporting Capital Gains Tax liabilities.
- SA102 (Employment): If you have income from employment.
- SA109 (Residence, Remittance Basis, etc.): If you’re claiming non-UK resident status or using the remittance basis.
Filling Tips:
- Be Honest and Accurate: Declare all your income. HMRC can check information against other sources. Ensure you meet tax compliance standards.
- Use Correct Boxes: Ensure figures are entered into the right sections. The online system helps guide this.
- Claim Allowable Expenses: Only claim expenses that are ‘wholly and exclusively’ for business purposes (for self-employment/property). Keep records to prove them. Use the Self Assessment Tax Calculator tool on GOV.UK for estimations.
- Check Calculations: If filing on paper, double-check your maths. The online system calculates tax automatically.
- Personal Allowance: Remember most people have a tax-free Personal Allowance (£12,570 for 2024/25).
Example Scenario: If you’re a freelancer earning £30,000 and have allowable business expenses of £5,000, your taxable profit is £25,000. You’d report this on the SA103.
Step 5: Review and Submit
Before hitting submit (online) or posting (paper):
- Review Everything: Read through your return carefully. Check for typos, missed sections, or incorrect figures.
- Get a Calculation: The online service will provide a tax calculation showing what you owe or if you’re due a refund.
- Save a Copy: Keep a digital or paper copy of your submitted return and your tax calculation for your records.
- Submit: Submit online via the Government Gateway or post your paper return well before the deadline. You’ll receive a submission receipt online.
Step 6: Common Mistakes to Avoid
- Missing the Registration Deadline: Register by 5 October if new to Self Assessment.
- Missing the Filing/Payment Deadline: Leads to automatic Self Assessment tax penalties. We can help if you’re dealing with HMRC investigations.
- Incorrect UTR/NI Number: Double-check these identifiers.
- Forgetting Income Sources: Declare all income (side hustles, interest, etc.).
- Incorrect Expense Claims: Only claim allowable expenses and keep proof. Don’t mix personal and business costs.
- Calculation Errors: Use the online system or double-check paper calculations.
- Not Including Supplementary Pages: Ensure all relevant income types are covered.
Paying Your Tax Bill
Once you’ve filed, you’ll know how much tax you owe. The main payment deadline is 31 January following the end of the tax year.
Payment Options:
- Online Banking/Direct Debit: The fastest, most secure way. Use your UTR number as the payment reference. Pay your Self Assessment tax bill via GOV.UK.
- Debit Card/Corporate Credit Card Online.
- At your Bank/Building Society: Requires a paying-in slip from HMRC.
- Cheque by Post: Allow time for processing.
Payments on Account:
If your Self Assessment tax bill is over £1,000 and less than 80% of your income was taxed at source (PAYE), you’ll usually need to make advance payments towards your next year’s tax bill. These are called ‘Payments on Account’.
- First Payment on Account: Due 31 January.
- Second Payment on Account: Due 31 July.
Each payment is typically 50% of your previous year’s bill. If your income changes significantly, you can apply to reduce your Payments on Account.
Difficulty Paying? (Time to Pay)
If you anticipate problems paying your tax bill by the deadline, don’t ignore it. Contact HMRC as soon as possible. You might be eligible for a Self Assessment Time to Pay arrangement, allowing you to spread the cost over manageable instalments. Penalties and interest may still apply, but engaging with HMRC is crucial. We can offer business advice if cash flow is a concern.
How Ask Accountants UK Ltd Can Help
Feeling overwhelmed by the Self Assessment process? From understanding the registration requirements and setting up your HMRC Government Gateway account, to meticulously gathering all the necessary documents and ensuring every figure is correct, it can certainly feel like a lot to handle. This is where seeking professional support can provide peace of mind and potentially save you money.
At Ask Accountants UK Ltd, we offer expert guidance tailored to your specific situation. Our services include:
- Registration and Setup: Assisting you with the initial Self Assessment registration and HMRC account setup, including troubleshooting login issues or recovering lost credentials.
- Document Preparation: Helping you identify, gather, and organise the financial records needed for an accurate return, potentially using cloud accounting tools.
- Tax Planning and Optimisation: Providing expert advice on identifying all allowable expenses and deductions relevant to your business or property income, aiming to legally minimise your tax liability through effective personal tax planning. We also offer strategic planning for future tax efficiency.
- Submission and Compliance: Professionally reviewing your completed Self Assessment return to catch potential errors or missed opportunities before submission. As professional tax compliance experts, we can also handle communications with HMRC, including support during HMRC investigations, ensuring compliance and minimising penalties.
- Specialised Services: Offering tailored advice for London residents, including tax-efficient strategies for freelancers and contractors in the gig economy, optimisation for landlord property tax regulations, and guidance for those navigating the complexities of international income.
By leveraging professional expertise from Ask Accountants UK Ltd, you can ensure your Self Assessment tax return is accurate, compliant, and submitted on time, reducing stress and avoiding potential penalties. Contact us today to discuss your needs.
Frequently Asked Questions (FAQs)
Here are answers to some common questions about the Self Assessment tax return:
- Who needs to file a Self Assessment tax return?
Generally, anyone with untaxed income over certain thresholds, like the self-employed, landlords, those with significant investment income, or those needing to pay Capital Gains Tax. Check the full list earlier in this guide or use the HMRC tool. - What is the deadline for registering for Self Assessment?
You must register by 5 October following the end of the tax year if you’ve never submitted a return before (e.g., 5 October 2025 for the 2024/25 tax year). See our business registrations service. - What are the main deadlines for submitting a Self Assessment tax return?
Paper returns are due by midnight 31 October. Online returns are due by midnight 31 January. The payment deadline is also 31 January. Check the tax calendar. - How do I calculate my taxable income for Self Assessment?
Add up all your relevant income sources (e.g., self-employment profits, rental income, interest). Then, deduct your tax-free Personal Allowance (£12,570 for 2024/25) and any allowable expenses or reliefs (like pension contributions or Self Assessment Tax Relief for job expenses). - What expenses can I claim on my Self Assessment?
If self-employed, claim allowable business costs (office supplies, travel, etc.). Landlords can claim property expenses (repairs, agent fees). You can also claim tax relief on pension contributions and qualifying charitable donations. Keep detailed records! Our tax planning services can help identify eligible expenses. - How do I pay my Self Assessment tax bill?
The easiest ways are via online banking, Direct Debit, or debit card through the HMRC Self Assessment login portal. Ensure you use your UTR as the reference. The deadline is 31 January. - What happens if I miss the Self Assessment deadline?
You’ll likely face automatic Self Assessment tax penalties, starting at £100 for missing the filing deadline, plus interest on unpaid tax. Penalties increase the longer the delay. We can assist if you face HMRC investigations or penalties.
Conclusion
Filing your Self Assessment tax return doesn’t have to be a source of stress. By understanding who needs to file, gathering your information early, being aware of the Self Assessment Tax Deadlines UK, and following the steps outlined above, you can navigate the process confidently.
Remember to:
- Register if you’re new to Self Assessment.
- Keep good records of income and expenses throughout the year.
- File online for ease and a later deadline.
- Declare all income accurately.
- Claim allowable expenses and reliefs.
- Submit and pay on time to avoid penalties.
If you’re unsure about anything, especially complex areas like Capital Gains Tax, foreign income, or significant self-employment expenses, consult the detailed guidance on the GOV.UK website or consider seeking advice from a qualified accountant like Ask Accountants UK Ltd. Our team offers comprehensive Self Assessment support and other accounting services. Filing accurately and on time ensures you meet your obligations and avoids unnecessary HMRC penalties. Good luck!
Disclaimer: This guide provides general information about UK Self Assessment tax returns for the 2024/25 tax year. Tax rules can change, and individual circumstances vary. Always refer to official HMRC guidance or consult a professional tax advisor for advice specific to your situation.
