Pillar Guide · Updated June 2026

UK Self Assessment Deadlines 2026/27: The Complete Tax Year Calendar

Self Assessment runs on a fixed annual calendar. Register by 5 October, file a paper return by 31 October, file online and pay your balancing payment by 31 January, and make payments on account by 31 January and 31 July. Missing any of these dates triggers automatic penalties and interest. This guide sets out every key date for the 2025/26 tax year, explains payments on account, the coding-out option, and how the penalty clock starts.

Last updated: 10 June 2026Last reviewed: 10 June 2026How we verify

Key Self Assessment dates -- 2026/27

Tax year: 6 April 2025 to 5 April 2026 (2025/26)
Register for SA: by 5 October 2026
Paper return: by 31 October 2026
Coding-out (file online): by 30 December 2026
Online return + balancing payment: by 31 January 2027
First payment on account: 31 January 2027
Second payment on account: 31 July 2026 (for 2025/26)

How the Tax Year Works

The UK tax year runs from 6 April to 5 April the following year. A Self Assessment return always covers one complete tax year. The 2025/26 return covers income earned between 6 April 2025 and 5 April 2026, and cannot be filed until the year has ended.

Once the year ends, HMRC issues a notice to file. The online service for that year opens in April. From then you have until the following 31 January to file online - giving roughly ten months. The deadlines below all hang off the 5 April year end.

Self Assessment applies to the self-employed, company directors with untaxed income, landlords, people with significant savings or dividend income, those affected by the High Income Child Benefit Charge, and anyone HMRC sends a notice to file.

Registration Deadline (5 October)

If you are newly within Self Assessment, you must tell HMRC by 5 October following the end of the tax year. For 2025/26 income, the registration deadline is 5 October 2026. Registration gives you a Unique Taxpayer Reference (UTR), without which you cannot file.

Failing to register on time is a "failure to notify" and can attract a penalty based on the "potential lost revenue" - the tax that should have been paid. The penalty is reduced or removed if you have a reasonable excuse or come forward voluntarily before HMRC contacts you. Register as soon as you know you have an obligation.

Paper Return Deadline (31 October)

If you file on paper, your return must reach HMRC by 31 October - three months before the online deadline. For 2025/26 that is 31 October 2026. Most taxpayers now file online, which is faster and gives an extra three months.

If you miss the paper deadline you can switch to filing online by 31 January and avoid a late filing penalty. If HMRC issued your notice to file after 31 July, you instead get three months from the date of the notice to file on paper.

Online Return and Payment (31 January)

The online filing deadline is midnight on 31 January. The balancing payment - the tax still owed after any payments on account - is due the same day. For 2025/26, both fall on 31 January 2027.

The 31 January date does double duty: it is the filing deadline for the online return and the payment deadline for the balancing payment plus the first payment on account for the next year. Filing and paying are separate obligations, each with its own penalty regime, so meeting one does not excuse missing the other.

Payments on Account

Payments on account are advance instalments towards next year's bill. They apply if your last Self Assessment liability exceeded GBP 1,000 and less than 80% of your tax was collected at source (for example through PAYE). Each instalment is 50% of your previous year's tax.

First payment on account: due 31 January, alongside the balancing payment.
Second payment on account: due 31 July.
Reducing payments: you can apply to reduce them if income is expected to fall, but HMRC charges interest if you reduce too far.

In your first year in Self Assessment, the 31 January payment can be a shock: you pay the full balancing payment for the year just ended plus the first 50% payment on account for the next year - effectively 150% of one year's tax in one go.

Coding Out (30 December)

If you owe less than GBP 3,000 and are employed or receive a pension, you can ask HMRC to collect the tax through your PAYE tax code over the following year, instead of paying a lump sum. To use this option you must file your online return by 30 December.

File online between 31 December and 31 January and you keep the right to file on time but lose the coding-out option - the tax becomes payable as a lump sum on 31 January. For people who would struggle with a lump sum, the 30 December date is the one to plan around.

When Penalties Start

Late filing penalties run on a fixed schedule from 31 January:

1 day late: GBP 100 fixed penalty, even if no tax is due.
3 months late: GBP 10 per day for up to 90 days (maximum GBP 900).
6 months late: the greater of GBP 300 or 5% of the tax due.
12 months late: a further GBP 300 or 5% of the tax due.

Late payment penalties are separate, charged at 30 days, 6 months and 12 months, each at 5% of the unpaid tax, plus daily interest from 1 February. Both filing and payment penalties can be appealed where there is a reasonable excuse.

Worked Examples

Example 1 - first year self-employed. Priya started self-employment in June 2025. Her 2025/26 tax and Class 4 NI come to GBP 4,000. She must register by 5 October 2026 and file online by 31 January 2027.

Balancing payment for 2025/26 (31 Jan 2027): GBP 4,000
First payment on account for 2026/27 (31 Jan 2027): GBP 2,000 (50%)
Total due 31 January 2027: GBP 6,000
Second payment on account (31 July 2027): GBP 2,000

Because her bill exceeds GBP 1,000 and little tax was collected at source, payments on account apply. Her first 31 January is the heaviest, at 150% of one year's tax.

Example 2 - missed deadline. Tom owes GBP 2,500 for 2024/25 but files his online return on 10 May 2026, just over three months late, and pays the same day.

Initial late filing penalty: GBP 100
Daily penalties (filing 3+ months late, approx. 9 days x GBP 10): approx. GBP 90
Late payment penalty (over 30 days, 5% of GBP 2,500): GBP 125
Plus daily interest on GBP 2,500 from 1 February 2026
Penalties before interest: approx. GBP 315

Had Tom met the 30 December date and owed under GBP 3,000, he could have coded the tax out through PAYE and spread it over 2026/27 with no lump sum at all.

Frequently Asked Questions

What is the main Self Assessment deadline for 2026?

The headline Self Assessment deadline is midnight on 31 January. For the 2025/26 tax year (ending 5 April 2026), you must file your online tax return and pay any tax owed by 31 January 2027. For the 2024/25 tax year (ended 5 April 2025), the online return and balancing payment were due by 31 January 2026. The 31 January date is both the filing deadline for online returns and the payment deadline for the balancing payment plus the first payment on account. Missing either triggers separate penalties and interest.

When do I have to register for Self Assessment?

You must register for Self Assessment by 5 October following the end of the tax year in which you first had untaxed income or a filing obligation. For example, if you started self-employment or received untaxed income during 2025/26 (the year ending 5 April 2026), you must register by 5 October 2026. Registration gives you a Unique Taxpayer Reference (UTR) and, for self-employed people, sets up Class 2 and Class 4 National Insurance. Late registration that causes you to miss the filing deadline can lead to a "failure to notify" penalty based on the tax due.

What is the deadline for a paper tax return?

Paper Self Assessment returns must reach HMRC by midnight on 31 October following the tax year end. For 2024/25 that was 31 October 2025; for 2025/26 it is 31 October 2026. This is three months earlier than the online deadline of 31 January. If you miss the paper deadline you can still file online by 31 January to avoid a late filing penalty. If HMRC issued your notice to file after 31 July, you instead get three months from the date of the notice to submit a paper return.

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What are payments on account and when are they due?

Payments on account are advance payments towards your next year's tax bill, each equal to 50% of your previous year's tax liability. They apply if your last Self Assessment bill was more than GBP 1,000 and less than 80% of your tax was collected at source. The first payment on account is due by 31 January (alongside the balancing payment), and the second is due by 31 July. For example, the second payment on account for 2025/26 is due 31 July 2026. You can apply to reduce payments on account if you expect your income to fall, but HMRC charges interest if you reduce them too far.

What happens if I miss the 31 January deadline?

Missing the 31 January online filing deadline triggers an immediate GBP 100 fixed penalty, even if you owe no tax or are due a refund. If the return is more than three months late, daily penalties of GBP 10 per day apply (up to 90 days, maximum GBP 900). At six months late there is a further penalty of the greater of GBP 300 or 5% of the tax due, and the same again at twelve months. Late payment of tax attracts separate late payment penalties at 30 days, 6 months and 12 months, plus daily interest. Penalties can be appealed if you have a reasonable excuse.

Is there a deadline to have tax collected through my tax code?

Yes. If you owe less than GBP 3,000 and are employed or receive a pension, you can ask HMRC to collect the tax through your PAYE tax code over the following year instead of paying a lump sum. To use this option you must file your online return by 30 December (not 31 January). Filing online between 31 December and 31 January means you lose the option to spread the tax through your code and must pay it as a lump sum by 31 January. The coding-out limit rises for higher earners but the GBP 3,000 figure applies to most taxpayers.

When does the tax year start and end?

The UK tax year runs from 6 April to 5 April the following year. The 2025/26 tax year started on 6 April 2025 and ends on 5 April 2026. Self Assessment returns relate to a single tax year: the 2025/26 return covers income earned between 6 April 2025 and 5 April 2026. HMRC normally issues notices to file shortly after the tax year ends, and the online filing system for a given year opens in April. You cannot file a return for a tax year until it has ended.

Can I file my return early, and is there any benefit?

Yes. You can file your online Self Assessment return any time from 6 April after the tax year ends, right up to 31 January. Filing early does not change your payment deadline - the balancing payment is still due 31 January - but it gives you certainty about the amount due, time to budget, and the chance to set up a Time to Pay arrangement or a Budget Payment Plan if needed. Early filing also reduces the risk of last-minute technical problems and means any repayment due to you is processed sooner.

What if the 31 January deadline falls on a weekend or bank holiday?

HMRC does not extend Self Assessment deadlines for weekends or bank holidays - the online system and payment channels remain available, so 31 January still applies even if it falls on a Saturday or Sunday. The only extensions HMRC has granted have been one-off concessions announced for specific exceptional circumstances, not a standing rule, so you should never assume a delay. Plan to file and pay a few days early to avoid being caught out.

Can I get more time to file if I have a reasonable excuse?

HMRC does not grant blanket deadline extensions, but if you miss 31 January because of a genuine reasonable excuse - such as a serious illness, bereavement, or a technical failure of HMRC's own systems - you can appeal the late filing penalty after it is issued. You must still file as soon as possible and explain the delay when appealing; simply forgetting or finding it too complicated does not count as a reasonable excuse. Appeals are made online or by post within 30 days of the penalty notice.

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About the author

Emma Clarke

UK Tax Writer

Emma Clarke has been writing about UK personal tax since 2018, with a particular focus on Self Assessment, PAYE coding and the practical mechanics of how HMRC actually applies the rules to ordinary salaries. Her work concentrates on translating the dense language of HMRC manuals and Finance Act schedules into worked examples that show, pound by pound, how income tax and National Insurance reduce a gross salary to the figure that lands in a UK bank account. Emma covers the full PAYE lifecycle: tax codes (1257L, BR, K codes, emergency codes), the Marriage Allowance, the High Income Child Benefit Charge, salary sacrifice arrangements and their effect on pensionable pay, the Apprenticeship Levy, and the differences between the rUK and Scottish income-tax regimes. She is particularly interested in the edge cases that catch PAYE employees out — the £100,000 personal-allowance taper, the 60% effective marginal rate it creates, and the interaction between student-loan plans and pension contributions. Every figure in Emma's articles is verified against the current HMRC rates pages and worked through a Self Assessment calculation by hand before publication. She writes to CalcHub's editorial standards: primary-source citations, plain English, no promotional language, and clear "this is general information, not financial advice" disclaimers where appropriate.

Personal-finance writer since 2018
UK tax specialism — PAYE, Self Assessment, National Insurance
Writes to CalcHub editorial standards (primary-source citation, annual review)

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Last updated: 10 June 2026How we verify

Disclaimer: This guide reflects UK Self Assessment deadlines for 2026/27as of June 2026. Dates that fall on a weekend or bank holiday are not extended by HMRC, so plan to pay and file in good time. This is general information, not financial advice. See gov.uk Self Assessment deadlines for HMRC's current published dates.