The Self Assessment deadline for the 2025/26 tax year is 31 January 2027. That is under three months away, and HMRC does not send a polite reminder before it charges you.
Most people who get a penalty did not mean to ignore the deadline. They simply left it. A missing form, a login that no longer works, a pile of receipts from last April. Each one eats a day, then a week, and suddenly it is the last night of January and the HMRC website is crawling.
This guide gives you the dates, the penalties, a document checklist and a clear way to get the return filed. If you would rather hand it over, our team at Budget Accountants in Ashford works as a Self Assessment tax return accountant for sole traders, landlords, directors and employees with extra income, and files returns every year.
When Is the Self Assessment Deadline for 2025/26?
The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. Your online return and any tax you owe must reach HMRC by 11:59 pm on 31 January 2027.
Key Dates to Put in Your Diary
- 5 October 2026: the deadline to register for Self Assessment if you were new to it. If you missed this one, register now. Do not wait.
- 31 October 2026: the deadline for paper returns. It has passed, so online is your only route.
- 30 December 2026: the last day to file online if you want HMRC to collect a balance of under £3,000 through your PAYE tax code, if you are eligible.
- 31 January 2027: the deadline to file online, pay your 2025/26 tax bill and make your first payment on account for 2026/27.
- 31 July 2027: the second payment on account.
Filing Early Does Not Mean Paying Early
You could have filed your 2025/26 return from 6 April 2026. Filing early gives you a clear tax bill months ahead and a faster refund if HMRC owes you. It does not move the payment date. The money is still due on 31 January.
Who Has to File a Self Assessment Tax Return?
You need to file if any of these apply to you:
- You were self-employed as a sole trader or in a partnership.
- You receive rental income from property.
- You had untaxed income above £2,500, such as casual work, savings interest or foreign income.
- Your income was over £100,000.
- You are a company director who takes dividends or has other income outside PAYE.
- You need to claim back tax or report capital gains from selling shares or property.
If you are unsure, check your HMRC letters or ask us. A five-minute call is cheaper than a £100 penalty.
Directors and Landlords Get Caught Out the Most
Directors assume the company accountant has dealt with everything. Often the company accounts are done but the personal return was never discussed. Landlords assume that because the rent goes through an agent, HMRC already knows. It does not work that way. Your personal return is your responsibility, and the penalty lands on you, not on your company or your agent.
Self Assessment Penalties: What Happens If You Miss 31 January 2027?
HMRC runs two separate penalty systems at once. One punishes late filing. The other punishes late payment. You can trigger both.
Late Filing Penalties
The day after the deadline you get an automatic £100 penalty. It applies even if you owe nothing, and even if you have already paid in full.
Then it climbs. After three months, HMRC adds £10 a day for up to 90 days, which is another £900. At six months and again at twelve months, there is a further charge of 5% of the tax due or £300, whichever is greater.
Late Payment Penalties
Pay late and HMRC charges 5% of the unpaid tax at 30 days, again at six months and again at twelve months. Interest runs on top from 1 February.
What a Seven Month Delay Costs
Take someone who owes £4,000 and files and pays seven months late.
- Initial filing penalty: £100
- Daily penalties after three months: £900
- Six month filing charge: £300
- Late payment charges at 30 days and six months: £400
That is about £1,700 in penalties on a £4,000 bill, before interest. Filing a day late and filing a year late are both bad, but the cost climbs fast, so the sooner you act the cheaper it is.
Documents to Gather Before You Start
The return itself takes a couple of hours when your paperwork is ready. It takes days when it is not. Collect these first.
Your Login and Identity Details
You need your Unique Taxpayer Reference, your National Insurance number and your Government Gateway user ID and password. If you have lost the login, start the recovery process today. HMRC sends activation codes by post, and that can take up to ten working days.
Income Records
Bring everything that counts as income for 6 April 2025 to 5 April 2026:
- Sales invoices or a bank statement summary for self employed income
- Rental statements, agent reports and mortgage interest figures
- Your P60 or P45 and any benefits in kind
- Dividend vouchers and company dividend records
- Bank and building society interest certificates
- Records of any shares, crypto or property you sold
Expenses and Reliefs
This is where people leave money behind. Gather receipts for business costs, mileage logs, home office costs, professional fees and equipment. Add pension contributions, Gift Aid donations and any Marriage Allowance details. A good accountant knows what is allowable and what will raise a question, so the return is accurate and you do not overpay.
How to File Your Return in Four Steps
Step 1: Register or Recover Your Account
Log in to your Government Gateway account. If you have never filed before, register for Self Assessment first and wait for your UTR to arrive.
Step 2: Add Up Income and Costs
Total your income by source, then list your allowable expenses. Keep it tidy. A simple spreadsheet or accounting software file by month saves hours.
Step 3: Complete and Check the Return
Fill in each section, then check the figures against your records. Pay particular attention to the tax code, student loan repayments and dividend amounts, because errors there are common.
Step 4: Submit and Pay
Submit online and keep the confirmation. Then pay the full amount by 31 January 2027, including the first payment on account if one applies. Bank transfer, debit card and Direct Debit all work, but allow time for the money to arrive. A transfer made on 31 January can miss the cut off time.
Payments on Account: The Bill Nobody Warns You About
If your last Self Assessment bill was over £1,000 and less than 80% of it was collected through PAYE or other deductions at source, HMRC asks you to pay in advance towards next year’s tax. These are called payments on account. They are two instalments, each worth half of last year’s bill, due on 31 January and 31 July.
In practice, your January bill is bigger than most people expect. You pay what you owe for 2025/26 and the first instalment for 2026/27 together. If your income fell this year, you can apply to reduce the payments. If you ignore this, you may end up lending HMRC money for six months. Check the figure before you file, not after.
Should You Do It Yourself or Hire a Self Assessment Accountant?
If you have one job and a bit of interest, do it yourself. HMRC’s online form is fine for that.
If you are self employed, run a limited company, own property or sold an asset, I would not bother. The time you spend learning the rules, hunting for the right box and second guessing each figure is worth more than a fixed fee. A mistake can also cost far more than the fee.
A specialist also keeps you ahead of change. From 6 April 2026, Making Tax Digital applies to sole traders and landlords with qualifying income over £50,000, and the threshold drops to £30,000 in April 2027. Your 2025/26 return is still the traditional annual return, but the way you keep records from now on is different. It is much easier to set that up with a professional than to rebuild your records halfway through the year.
At Budget Accountants, our ACCA and AAT qualified team works as your personal tax accountant. We prepare your return, check every allowance and file it before the deadline. Pricing is fixed and clear, with no surprises after the work is done.
Conclusion
The 31 January 2027 deadline is fixed and the penalties are automatic. Gather your paperwork this month, check your login now and work out your payment date before you file. If your affairs are anything more than simple, get a tax return accountant involved in November rather than January.
Ready to hand it over? Call us on 07540 460675, email info@budgetaccountants.co.uk or book a free consultation. We serve Ashford, Staines, Feltham, Sunbury and the rest of Surrey and Middlesex, and we work with clients online across the UK.
Frequently Asked Questions
What is the Self Assessment deadline for the 2025/26 tax year?
The deadline to file online and pay any tax owed is 31 January 2027. The paper deadline was 31 October 2026, so online filing is now your only option.
Do I have to file if I owe no tax?
If you are required to file, yes. HMRC charges the £100 penalty for a late return even when the tax bill is zero.
What if I have missed the deadline to register for Self Assessment?
The registration deadline was 5 October 2026. Register as soon as you can. Delay pushes your UTR and your filing closer to the January deadline, and HMRC can issue separate penalties for failing to notify.
Can I get more time to file?
HMRC does not offer extensions as standard. You can appeal a penalty if you have a reasonable excuse, such as serious illness or a bereavement, but you should not count on it.
How long does it take to complete a return?
With organised records, a simple return can take one to two hours. Returns with property, dividends, capital gains or several income sources take longer, which is why an early start matters.
How much does a Self Assessment accountant cost?
The cost depends on how many income sources you have and how tidy your records are. Budget Accountants offers fixed, transparent pricing and a free initial consultation, so you know the fee before any work begins.
Can I pay my tax bill in installments?
If you cannot pay in full, contact HMRC before the deadline to ask about a Time to Pay arrangement. Filing on time still matters, because it avoids the filing penalties even if payment has to be spread.
