# 30 December 2026: the Self Assessment filing date for clients who want the tax collected through their PAYE code > File online by 30 December 2026 and HMRC can collect a balance under £3,000 through the 2027 to 2028 tax code. The conditions, a worked example and a timetable. - Page to cite: https://aeolookup.com/accountants/self-assessment-30-december-deadline-tax-code-paye/ - Publisher: AEO Lookup (https://aeolookup.com/) - Section: Accountancy practices, Deadlines and penalties - Published 1 October 2026 - Key fact: GOV.UK, read on 1 October 2026, says a 2025 to 2026 return filed online by 30 December 2026 lets HMRC collect a balance under £3,000 through the PAYE code from 6 April 2027. For an employee owing £1,860 that is £155 a month for 12 months; filed a day later, the same client pays £2,790 on 31 January 2027, which is the £1,860 plus a £930 payment on account. - Sources: GOV.UK "Self Assessment tax returns: Deadlines", "Pay your Self Assessment tax bill: Through your tax code" and "Understand your Self Assessment tax bill: Payments on account"; HMRC tax return notes SA150 for 2025 to 2026 (page TRG 15, box 2); Taxes Management Act 1970, section 59A (legislation.gov.uk); all read 2026-10-01. 30 December 2026 is the last day to file a 2025 to 2026 Self Assessment return online if the client wants HMRC to collect the tax through their PAYE code. A return filed on 31 December is still a month inside the main deadline, but the whole balance is then due on 31 January 2027. For a paper return the equivalent date is 31 October 2026. **Free tool on the page:** 30 December records request email maker. It runs in the browser at https://aeolookup.com/accountants/self-assessment-30-december-deadline-tax-code-paye/#tool and asks for no sign-up. ## The conditions GOV.UK's page on paying through a tax code, read on 1 October 2026, sets three conditions. All must be met: 1. the client owes less than £3,000 on the tax bill; 2. the client already pays tax through PAYE, for example as an employee or on a company pension; 3. the online return is submitted by 30 December. HMRC then collects the tax automatically, unless the return asks it not to. On the paper form that is an X in box 2 on page TR 6. HMRC's notes to the 2025 to 2026 return say collection runs through wages or pension from 6 April 2027, and GOV.UK says it is taken in equal instalments over 12 months. ## When HMRC will not code it out GOV.UK lists four cases where the client cannot pay this way: - there is not enough PAYE income to collect it from; - the client would pay more than 50% of their PAYE income in tax; - the client would end up paying more than twice as much tax as they normally do; - the client owed £3,000 or more and made a part payment to get under the limit. Class 2 National Insurance cannot be collected through the code either. Where it is due, it is paid by 31 January 2027. ## A worked example A client earns £34,000 from a job and made a rental profit of £9,300 in 2025 to 2026. Total income of £43,300 sits inside the basic rate band, so the rental profit is taxed at 20%: £9,300 × 20% = £1,860. PAYE has already taken tax on the salary: (£34,000 − £12,570) × 20% = £4,286 a year, or £357.17 a month. | | Filed online by 30 December 2026 | Filed 31 December 2026 to 31 January 2027 | |---|---|---| | Due on 31 January 2027 | £0 | £2,790 | | Due on 31 July 2027 | £0 | £930 | | From pay, April 2027 to March 2028 | £155 a month extra | Nothing extra | The £155 is £1,860 ÷ 12. It takes the monthly deduction to £512.17, which is less than twice the usual £357.17, so the doubling test is met. The £2,790 needs explaining. GOV.UK says payments on account are due unless last year's bill was under £1,000 or more than 80% of the tax owed was paid outside Self Assessment. Here the total tax is £6,146 (£4,286 + £1,860) and PAYE covered £4,286 of it, which is 69.7%. So a client who pays the balance directly owes £1,860 on 31 January 2027, a first payment on account of £930 for 2026 to 2027 the same day, and a second £930 on 31 July 2027. A balance collected through the code is treated differently. Section 59A(8) of the Taxes Management Act 1970 counts amounts "to be deducted at source under PAYE regulations in subsequent years" as tax deducted at source. With the £1,860 coded out, the tax left to pay directly is nil and no payments on account arise. The tax is the same either way. What changes is when it leaves the client's bank account: £2,790 in one day, or £155 a month starting three months later. ## Which clients to pull from the list Run the client list for people who have both PAYE income and a small untaxed source: - employees and pensioners with one rental property; - employees with a side business; - directors with a salary and a small dividend; - clients paying the High Income Child Benefit Charge through their return. Leave out anyone likely to owe £3,000 or more, since a part payment does not bring them under the limit. Leave out anyone who has said they would rather pay in January. And check last year's bill: a client whose code already carries a balance from 2024 to 2025 may have less room under the doubling test. ## A timetable that ends before Christmas 30 December 2026 is a Wednesday in a week when few clients answer email. Set an internal filing date of Friday 18 December and count back using the three stages in our [records request letter template](https://aeolookup.com/accountants/records-request-letter-template-accountants/): | Step | Date | |---|---| | First records request (24 days before filing) | Tuesday 24 November 2026 | | Reminder (14 days before) | Friday 4 December 2026 | | Final letter (7 days before) | Friday 11 December 2026 | | Practice files | Friday 18 December 2026 | | HMRC's cut-off | Wednesday 30 December 2026, 11:59pm | ## What to tell the client > Subject: Send your tax records by 4 December and spread the bill over next year > > If we file your 2025 to 2026 tax return online by 30 December 2026, HMRC can collect what you owe through your tax code from April 2027, in 12 monthly amounts taken from your pay. We estimate your bill at [£1,860], or about [£155] a month. > > If we file after 30 December, the full amount is due on 31 January 2027, and HMRC may also ask for a payment towards next year's bill on the same day. > > To file in time we need [your rental income and expenses] by Friday 4 December 2026. ## After filing HMRC's notes say it will try to collect through the code, not that it will. Check the client's 2027 to 2028 coding notice when it arrives in the new year. If the balance is not in the code, it is due on 31 January 2027, and the penalties in our [Self Assessment penalty calculator](https://aeolookup.com/accountants/self-assessment-late-filing-penalty-calculator/) apply from that date. A client who registered late this year has a different set of dates, set out in our guide to [registering for Self Assessment after 5 October](https://aeolookup.com/accountants/what-happens-if-client-registers-self-assessment-late/). Overlyft ![](https://aeolookup.com/img/d/ours-badge.png) can set up an AI assistant that holds each client's filing dates and sends the records requests on the days above once a partner has approved the wording. The return, the estimate and the advice stay with the accountant. This is general information, not professional advice. ## Short answers from this page **What is the 30 December Self Assessment deadline for?** A 2025 to 2026 return filed online by 30 December 2026 lets HMRC collect a balance under £3,000 through the client's PAYE tax code from 6 April 2027, in 12 equal instalments. The client must already pay tax through PAYE. Filed after that date, the whole balance is due on 31 January 2027. --- ![](https://aeolookup.com/img/d/owner-line.png) General information for UK small firms, not legal, tax or financial advice.