Every autumn we speak to people across Belfast who know their tax return is due “sometime in January” and plan to deal with it after Christmas. The return itself is often straightforward. What causes the stress is finding out in mid-January what the bill is, and that it may be larger than expected because of payments on account.

This guide covers the 2025-26 tax year (6 April 2025 to 5 April 2026): the key dates, who needs to file, what happens if you miss a deadline, and what to gather now so you can file in the autumn and simply pay in January.

Key Self Assessment dates for 2025-26

Date What is due
5 October 2026 (now passed) Deadline to tell HMRC you need to file, if you have not filed before or did not need to for 2024-25
31 October 2026 Paper tax return deadline (11:59pm)
30 December 2026 Online deadline if you want tax owed collected through your PAYE tax code (11:59pm)
31 January 2027 Online tax return deadline, payment of any 2025-26 tax owed (the balancing payment) and first payment on account for 2026-27 (11:59pm)
31 July 2027 Second payment on account for 2026-27

The 5 October registration date has now passed. If you needed to register for 2025-26 and have not, do it now. HMRC says you could get a penalty if you tell them after 5 October 2026, and you will need your Unique Taxpayer Reference (UTR) before you can file, which takes time to arrive. If you have missed the date, we can help you register and get the return in on time.

The 30 December date is worth knowing if you are employed or receive a company pension. If you owe less than £3,000, already pay tax through PAYE and file online by 30 December, HMRC can collect the tax through your tax code in monthly instalments over the following year instead of asking for a lump sum in January.

For the wider calendar, including VAT, payroll and company deadlines, see our key tax dates for NI businesses in 2026-27.

Who needs to file a Self Assessment tax return?

GOV.UK says you must send a return for 2025-26 if, during the tax year:

  • you were self-employed as a sole trader and earned more than £1,000
  • you were a partner in a business partnership
  • you had to pay Capital Gains Tax when you sold or disposed of something
  • you had to pay the High Income Child Benefit Charge and do not pay it through PAYE

You may also need to file if you had other untaxed income, such as rental income, tips and commission, savings interest, dividends or foreign income.

If all your income is taxed through PAYE, you often will not need a return. HMRC’s online tool, check if you need to send a Self Assessment tax return, is the quickest way to confirm your own position for 2025-26.

The High Income Child Benefit Charge

If you or your partner earned more than £60,000 and one of you claimed Child Benefit, some of it has to be paid back: 1% for every £200 over £60,000, rising to all of it at £80,000 or more. Employed people can now pay the charge through PAYE without registering for Self Assessment. If you already file a return for another reason, the charge goes on your return.

Common situations we see in NI

Landlords

Rental income is untaxed, so most landlords file a return. Keep a record of rent received and the costs you are claiming, such as letting agent fees, repairs, insurance and mortgage interest. Our property and landlords page covers the wider picture.

Sole traders and tradespeople

If your self-employed income was more than £1,000, you need to file. Your return pulls together sales, expenses and any equipment you bought. Many of the tradespeople we work with find the hardest part is simply gathering a year of receipts, so start that now.

Company directors with dividends

Directors who take dividends above their tax-free allowance, or who have other income alongside their salary, usually need a return. If you are planning next year’s pay, our guide to directors’ salary versus dividends is a useful read.

Capital gains and the 60-day rule

If you sold a UK residential property and had Capital Gains Tax to pay, you should already have reported and paid it within 60 days of completion using HMRC’s separate property service. If you are registered for Self Assessment, GOV.UK says you also need to include the sale on your tax return, and the tax already paid is taken into account. Gains on other assets, such as shares, are reported on the return itself.

Late filing and late payment penalties

HMRC’s penalties for a late return are:

  • £100 as soon as the return is late, even if there is no tax to pay
  • after 3 months, £10 a day, up to a maximum of £900
  • after 6 months, a further 5% of the tax due or £300, whichever is greater
  • after 12 months, another 5% of the tax due or £300, whichever is greater

Paying late is charged separately. HMRC adds a penalty of 5% of the unpaid tax at 30 days, 6 months and 12 months after the deadline, and charges interest on the amount owed. Late payment interest is currently set at the Bank of England base rate plus 4%.

If you cannot pay in full, contact HMRC before the deadline. Filing on time still avoids the filing penalties, even if the payment follows later.

Payments on account, explained simply

Payments on account are advance payments towards next year’s tax. Each is half of the previous year’s bill, due on 31 January and 31 July.

You do not have to make them if last year’s bill was less than £1,000, or if you paid more than 80% of your tax outside Self Assessment (for example through your tax code).

A simple example. Say this is your first year with a bill, and your 2025-26 tax comes to £6,000. By 31 January 2027 you pay:

  • £6,000 balancing payment for 2025-26, plus
  • £3,000 first payment on account for 2026-27

That is £9,000 in January, followed by another £3,000 on 31 July 2027. This first-year jump is the one that catches people out. If your income for 2026-27 has fallen, you can ask HMRC to reduce your payments on account, but if you reduce them too far you will pay interest on the shortfall.

How Making Tax Digital fits in

If your qualifying income (self-employment and property income before expenses) was over £50,000 for 2024-25, you should have started using Making Tax Digital for Income Tax from 6 April 2026. That changes how you keep records and report for 2026-27 onwards.

It does not change your 2025-26 return. HMRC is clear that you still submit a Self Assessment tax return for the tax year before you start using Making Tax Digital, so the 2025-26 return is filed in the usual way by 31 January 2027. Your first Making Tax Digital tax return will be for 2026-27, due by 31 January 2028. The quarterly updates you send during 2026-27 are separate from this annual return, and our MTD deadline calendar sets out those dates.

The threshold drops to £30,000 from 6 April 2027 (based on your 2025-26 income), so the figures on this year’s return may decide whether you join next year. Our guides on when Making Tax Digital starts for you and our Making Tax Digital service explain what to expect.

Records checklist for your 2025-26 return

Gather these now, for 6 April 2025 to 5 April 2026:

  • your UTR and Government Gateway login
  • P60 and any P45 from employment, and P11D if you had benefits in kind
  • pension statements, including any State Pension
  • self-employed sales and expenses, with receipts and bank statements
  • rental income and letting costs, including mortgage interest statements
  • dividend vouchers and bank or building society interest
  • details of any assets sold, with purchase and sale costs, and any 60-day property report already filed
  • personal pension contributions and Gift Aid donations
  • Child Benefit details if the High Income Child Benefit Charge applies
  • any student loan details
  • a note of payments on account already made for 2025-26

File in the autumn, pay in January

You do not have to pay when you file. If you submit your return in October or November, you still pay by 31 January 2027, but you know the exact figure weeks in advance. That gives you time to set the money aside, to check whether payments on account can be reduced, and, if you are on PAYE and owe less than £3,000, to file by 30 December so the tax can be collected through your tax code.

Filing early also means any refund owed to you arrives sooner, and any queries from HMRC or missing paperwork are dealt with before the January rush.

How Arro Group can help

We prepare and file Self Assessment returns for landlords, sole traders, directors and individuals across Belfast and Northern Ireland. We gather your figures, check the expenses and allowances you can claim, tell you exactly what is due and when, and file the return with HMRC. If you missed the 5 October date, we can help you register with HMRC first. If Making Tax Digital applies to you from 2026-27, we can take care of that too: we deal with the software as part of our service, and the only step at your end is the bank feed, which we organise.

Find out more about our personal tax service, or get in touch with our Belfast team to get your 2025-26 return sorted well before January.