Self Assessment Tax Return Period: UK Deadlines, Penalties & Filing Guide
Confused about when the self assessment tax return period starts and ends? Missing HMRC deadlines can cost you £100s in penalties. This expert guide explains every UK self assessment deadline for 2025/26 and 2026/27. Learn how to file your self assessment online and avoid late filing fees with Eternity Accountants.
Key Takeaways
- The UK tax year runs from 6 April to 5 April the following year.
- Paper self assessment returns are due by 31 October; online by 31 January.
- HMRC issues a £100 penalty for late returns, rising to £1,600+ with delays.
- Landlords, sole traders, and directors may all need to file self assessment.
- Making Tax Digital for ITSA is mandatory.
Need help meeting self assessment deadlines or filing online? Call 0116 4030595 or email info@eternityaccountants.co.uk for a free consultation.
Understanding the Self Assessment Tax Return Period
The self assessment tax return period aligns with the UK tax year, not the calendar year. Every penny of income and allowable expense between 6 April and 5 April must be reported to HM Revenue & Customs (HMRC).
The 12-month period from 6 April to 5 April, covering all taxable income and expenses for that tax year.
When does the UK tax year start and end?
The UK tax year starts on 6 April and ends on 5 April the following year. For example, the 2025/26 tax year covers 6 April 2025 to 5 April 2026.
Why does the tax period matter for self assessment?
This period determines which income and expenses you must declare. Reporting outside the correct period can lead to underpayment or overpayment, triggering HMRC investigations and penalties.
What income must be reported?
All untaxed income—self-employment, rental income, dividends, and more—earned during the tax year must be included. This applies whether you’re a sole trader, landlord, or company director.
| Tax Year | Start Date | End Date |
|---|---|---|
| 2025/26 | 6 April 2025 | 5 April 2026 |
| 2026/27 | 6 April 2026 | 5 April 2027 |
Quick Tip: Always check which tax year your income falls into—using the wrong period is a common mistake that can cost you.
Source: GOV.UK Self Assessment Deadlines
Q: When does the UK tax year start and end?
A: The tax year starts on 6 April and ends on 5 April the following year.Q: What is the self assessment tax period?
A: It is the 12-month period for which you report income to HMRC, matching the UK tax year.Q: Why is the tax period important?
A: It determines which income and expenses are included on your return.
Key Self Assessment Deadlines and HMRC Tax Return Dates for 2025/26 and 2026/27
| Tax Year | Paper Return Deadline | Online Return Deadline | Payment Deadline | First Penalty | Further Penalties |
|---|---|---|---|---|---|
| 2025/26 | 31 October 2026 | 31 January 2027 | 31 January 2027 | £100 fixed | £10/day after 3 months, 5%/£300 at 6 & 12 months |
| 2026/27 | 31 October 2027 | 31 January 2028 | 31 January 2028 | £100 fixed | £10/day after 3 months, 5%/£300 at 6 & 12 months |
All critical UK self assessment deadlines
- Register for self assessment by 5 October after your first trading year.
- Paper return deadline: 31 October following the tax year end.
- Online return and payment deadline: 31 January after the tax year end.
- Payments on account: 31 January and 31 July.
- Submit by 30 December if you want tax collected via PAYE code.
Paper vs online submission
Paper returns must reach HMRC by 31 October. Online returns offer more time, with a 31 January deadline. Most clients now file digitally, especially as Making Tax Digital (MTD) expands.
Deadlines for payments, amendments, and payments on account
Tax owed must be paid by 31 January. Payments on account (advance tax for the next year) are due 31 January and 31 July. Amendments to returns can be made up to 12 months after 31 January.
Quick Tip: Registering late means you can’t file online—leading to automatic penalties. Always register as soon as you start trading.
Source: GOV.UK Self Assessment Deadlines
Q: What are the UK self assessment deadlines?
A: Key deadlines are 31 October (paper) and 31 January (online and payment) after the tax year ends.Q: What happens if I miss the deadline?
A: You receive a £100 penalty with further penalties for continued delay.Q: When do I pay tax?
A: By 31 January after the tax year end, and payments on account by 31 January and 31 July.
Who Needs to Complete a Self Assessment? A Guide for Sole Traders, Landlords & Directors
Many new business owners wrongly assume PAYE employees never need to file. Actually, if you have rental income, dividends, or untaxed earnings, you’re likely required to file.
Sole traders and self-employed
Anyone earning over £1,000 from self-employment must register and file. Even part-time side hustles count. See our Self Assessment Service for full guidance.
Landlords and property income
If you receive more than £1,000 rental income in a tax year, you must report it. This applies to accidental landlords and those letting out a single room. See Landlord Accountants for tailored advice.
Company directors and other cases
Most directors must file if they receive dividends, untaxed income, or benefits-in-kind. Even if all your income is taxed at source, some directors are still required to complete a return.
- Sole traders: income over £1,000/year
- Landlords: rental income over £1,000/year
- Company directors: untaxed income/dividends
- Partners in a business partnership
- High earners (£100,000+)
Anyone with untaxed income, including sole traders, landlords, directors, high earners, and partners, must file a return if they meet HMRC criteria.
Quick Tip: Even if you’re a PAYE employee, you may need to file if you have rental, freelance, or foreign income.
Source: GOV.UK Who Must Send a Tax Return
Q: Who needs to do a self assessment return?
A: Sole traders, landlords, company directors, and anyone with untaxed income.Q: Do landlords have to file a tax return?
A: Yes, if you earn over £1,000 in property income.Q: Do directors need to file self assessment?
A: Most directors are required to file if they get untaxed income.
How to File Your Self Assessment Online: Step-by-Step Guide for 2026/27
Did you know? Over 1.5 million UK businesses are enrolled in Making Tax Digital (source: HMRC, 2026).
Registering for self assessment
Register online with HMRC by 5 October after your first trading year. You’ll receive a Unique Taxpayer Reference (UTR) and activation code.
Filling in your online return
Log in to your HMRC account or use MTD-compatible software (Xero, QuickBooks, FreeAgent, Sage). Enter your income, expenses, and any other required details. Double-check for accuracy before submitting.
Pre-submission checklist and common mistakes
- UTR and National Insurance number
- Income details (self-employment, property, dividends)
- Expense receipts and records
- Bank statements
- P60/P45 if also employed
Quick Tip: Use software to spot errors—manual entry is the #1 cause of HMRC penalties.
Real-world example: A Leicester freelancer started trading in July 2025 but missed the 5 October registration. With Eternity’s help, they registered, filed online by 31 Jan 2027, and avoided a £100+ penalty—paying £350 for accountancy versus £1,000+ in potential fines.
Source: GOV.UK Sending Your Return
Q: How do I register for self assessment?
A: Register online with HMRC by 5 October after your first trading year.Q: How do I file my self assessment online?
A: Log in to your HMRC account, complete your tax return, and submit online.Q: What do I need to file?
A: UTR, NI number, income and expense records, and relevant receipts.
Self Assessment Late Filing Penalties: What Happens If You Miss the Deadline?
Most guides fail to mention that penalties escalate rapidly—£100 on day one, then £10 per day after three months.
HMRC penalty structure explained
- £100 fixed penalty for missing the deadline by 1 day
- £10 per day up to £900 after 3 months
- 5% of tax due or £300 (whichever greater) at 6 and 12 months
- Interest charged on unpaid tax
Interest and further consequences
Interest accrues daily on unpaid tax. HMRC can also take enforcement action, including debt collection and court proceedings, if returns or payments are very late.
How to appeal or mitigate penalties
You can appeal if you have a reasonable excuse (illness, bereavement, HMRC online issues). Write to HMRC promptly and provide evidence.
Quick Tip: File even if you can’t pay—late filing penalties are separate from late payment penalties.
Source: GOV.UK Self Assessment Penalties
Q: What if I miss the self assessment deadline?
A: You get an automatic £100 penalty and further charges for continued delay.Q: How much are HMRC late filing penalties?
A: £100 fixed, then £10/day after 3 months, plus 5% of tax due or £300 after 6/12 months.Q: Can I appeal a penalty?
A: You can appeal if you have a reasonable excuse, such as illness or bereavement.
Industry-Specific Self Assessment Advice: Contractors, Landlords & More
62% of UK SMEs use an external accountant (source: ONS, 2026).
Contractors and freelancers
As a contractor or freelancer, declare all untaxed income and claim allowable expenses. IR35 status may affect your obligations—see our Freelance Accountants page.
A set of HMRC rules to determine if a contractor is genuinely self-employed or should be taxed as an employee.
Landlords and property owners
If you’re a landlord, include all rental income and claim allowable expenses (e.g., mortgage interest, repairs). See our Landlord Accountants for more.
Directors and limited companies
As a limited company director, include salary, dividends, and any other untaxed income. See our Limited Company Accountants for advice on director obligations.
- Contractors: declare all contracts, check IR35 status
- Landlords: report gross rents, deduct allowable costs
- Directors: include all income sources—salary, dividends, benefits
Quick Tip: Industry rules change often—review HMRC updates annually to maximise reliefs.
Source: GOV.UK Who Must Send a Tax Return
Q: Do contractors need to file self assessment?
A: Yes, for untaxed income and to declare expenses.Q: How does self assessment work for landlords?
A: Declare rental income and allowable expenses if earning over £1,000.Q: What must directors include?
A: Salary, dividends, and any untaxed income.
Software for Self Assessment: Xero, QuickBooks, FreeAgent, and Sage
MTD for ITSA becomes mandatory from April 2026 for £50k+ income—one of the biggest changes in UK tax since Self Assessment began.
Benefits of accounting software
- Automates calculations and reduces human error
- Links directly to HMRC for digital tax returns
- Tracks income, expenses, and deadlines
How to use software for self assessment
- Choose an HMRC-recognised provider (Xero, QuickBooks, FreeAgent, Sage)
- Connect your bank accounts and upload records
- Review suggested figures and submit directly to HMRC
| Software | MTD Ready | Direct HMRC Submission | Expense Tracking | Bank Feeds |
|---|---|---|---|---|
| Xero | Yes | Yes | Yes | Yes |
| QuickBooks | Yes | Yes | Yes | Yes |
| FreeAgent | Yes | Yes | Yes | Yes |
| Sage | Yes | Yes | Yes | Yes |
Quick Tip: Choose software with direct HMRC integration for a smoother, error-free submission.
Source: GOV.UK MTD Software List
Q: Which software is MTD-compliant?
A: Xero, QuickBooks, FreeAgent, and Sage are all HMRC-recognised for self assessment.Q: When is MTD for ITSA mandatory?
A: April 2026 for £50k+ income, April 2027 for £30k+, April 2028 for £20k+.Q: What are the benefits of using software?
A: Saves time, reduces errors, and ensures HMRC compliance.
How to Find an Accountant Near You for Self Assessment
Choosing a local accountant offers face-to-face advice and city-specific expertise—especially valuable for complex tax returns.
Why local expertise matters
Local accountants understand regional industries and can meet in person. For example, an accountant in Leicester may specialise in East Midlands property or manufacturing sectors.
What to look for in a self assessment accountant
- ICAEW, ACCA, or AAT accreditation
- Transparent fees (from £7.50/month at Eternity Accountants)
- Strong Google Reviews and local presence
- Experience with your industry
| Factor | Online Accountant | Local Accountant |
|---|---|---|
| Cost | Lower | Higher |
| Meetings | Virtual | Face-to-face |
| Availability | Flexible | Office hours |
| Nationwide Support | Yes | Limited |
City-specific support: Leicester, London, and beyond
Looking for an accountant in Leicester? Eternity Accountants, 6 Egginton Street, Leicester, LE5 5BA, offers local expertise and face-to-face service. In London, you’ll find a chartered accountant near you with specialist knowledge of city regulations. Our clients in Birmingham benefit from industry-specific support, while those in Manchester and Nottingham enjoy tailored advice for local property and tech sectors. As an East Midlands accountant, we also support clients across Derby, Lincoln, and Northampton.
Find a recognised accountant on GOV.UK
Q: How do I find an accountant for self assessment?
A: Use ICAEW, ACCA, or AAT directories and check local reviews.Q: Why use a local accountant?
A: For tailored advice and in-person meetings.Q: Which cities do you serve?
A: Leicester, London, Birmingham, Manchester, Nottingham, East Midlands.
How to Verify an Accountant
| Check | Why It Matters |
|---|---|
| ICAEW Registration | Regulation |
| Practising Certificate | Legal permission |
| Professional Indemnity Insurance | Client protection |
| Google Reviews | Reputation |
| Engagement Letter | Service clarity |
| HMRC Agent Status | HMRC representation |
5-Step Accountant Selection Process
- Identify your needs: Are you a sole trader, landlord, or company director?
- Shortlist 3 accountants: Compare local and online options.
- Verify regulation: ICAEW, ACCA, or AAT membership.
- Compare pricing: Check fixed fees and inclusions.
- Book consultation: Speak to your chosen accountant before committing.
When Should You Change Accountant? 5 Warning Signs
- Slow communication and unreturned calls
- Repeated filing errors or missed deadlines
- Lack of proactive tax planning or advice
- No Making Tax Digital support
- Unclear or rising fees without explanation
Questions Your Accountant Should Ask You
- Are you VAT registered?
- Do you employ staff?
- Do you receive dividends?
- Do you own rental property?
- Do you expect income growth?
UK Accountancy Statistics
- Over 93,000 chartered accountants in the UK (ICAEW, ACCA, CIMA, AAT)
- 1.5 million+ businesses enrolled in Making Tax Digital
- 800,000+ HMRC late filing penalties issued in 2024/25
- 62% of UK SMEs use an external accountant
Self Assessment Deadlines and Penalties: 2025/26 vs 2026/27
| Tax Year | Paper Return Deadline | Online Return Deadline | Payment Deadline | First Penalty | Further Penalties |
|---|---|---|---|---|---|
| 2025/26 | 31 October 2026 | 31 January 2027 | 31 January 2027 | £100 fixed | £10/day after 3 months, 5%/£300 at 6 & 12 months |
| 2026/27 | 31 October 2027 | 31 January 2028 | 31 January 2028 | £100 fixed | £10/day after 3 months, 5%/£300 at 6 & 12 months |
DIY vs Professional Self Assessment: Which Is Right for You?
| Factor | DIY (HMRC Online) | Professional Accountant |
|---|---|---|
| Cost | £0-£20 | £100-£800+ |
| Time | 5-10 hours+ | 1-2 hours |
| Error Risk | High (no checks) | Low (checked by expert) |
| Tax Planning | None | Optimised |
Fee ranges: Simple Employee Return £100-£250, Self-Employed Sole Trader £150-£500+, Landlord £150-£600+, Company Director £200-£800+
Decision Tree: What Do You Need? → Who to Speak To?
| Need | Who to Speak To |
|---|---|
| Tax Return | Accountant |
| VAT Advice | Accountant |
| Corporation Tax | Accountant |
| Pension Transfer | FCA Adviser |
| Investment Advice | FCA Adviser |
| Mortgage Advice | Mortgage Adviser |
How to Find an Accountant Near You
Searching for an “accountant near me” brings up hundreds of options. Eternity Accountants, 6 Egginton Street, Leicester, LE5 5BA, 0116 4030595, is your trusted local accountant UK-wide. Whether you need a chartered accountant near me for a complex return or a local accountant in Leicester, London, Birmingham, Manchester, Nottingham, or the wider East Midlands, we offer tailored support.
Our Google Business Profile is rated 4.9/5 by hundreds of clients. Read verified reviews to see how we’ve helped clients in every major UK city meet deadlines and save money.
Quick Tip: Always check for ICAEW, ACCA, or AAT accreditation before appointing an accountant.
Next Steps
- Download our Self Assessment Checklist to prepare your documents.
- Book a free consultation to discuss your tax return for 2025/26 or 2026/27—call 0116 4030595 or email info@eternityaccountants.co.uk.
- Switch to Eternity Accountants for fixed-fee, MTD-ready self assessment support.
Quick Answers
- When does the UK tax year start? 6 April each year.
- What is the deadline for online self assessment? 31 January after the tax year ends.
- How much is the penalty for late filing? £100 fixed, then daily and further penalties apply.
- Who must file a self assessment tax return? Sole traders, landlords, directors and anyone with untaxed income.
- Which software is compatible with HMRC for self assessment? Xero, QuickBooks, FreeAgent, Sage.
- How much should I pay an accountant? Typical fees range from £100-£800+ depending on your situation; see our Accountant Pricing page for details.
Ready to get your self assessment sorted? Call 0116 4030595 or email info@eternityaccountants.co.uk for a free, no-obligation quote today.
Why Choose Eternity Accountants?
- ICAEW regulated
- AAT accredited
- Fixed fees from £7.50/month
- Making Tax Digital compliant
- Dedicated accountant
- UK-wide service
- Leicester based
- Free initial consultation
Want expert help with your self assessment tax return period? Contact Eternity Accountants for a free initial consultation. Call 0116 4030595 or email info@eternityaccountants.co.uk.
