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When Is the Self Assessment Deadline for 2025/26?

Quick answer: For the 2025/26 tax year, which ended on 5 April 2026, you must file online and pay what you owe by midnight on 31 January 2027. The paper deadline was much earlier, midnight on 31 October 2026, and has now passed, so if you have not filed yet, file online. The deadline to register for Self Assessment for that year was 5 October 2026 and has already passed, so if you have not registered yet you should do it now rather than wait. Miss 31 January and there is an automatic £100 penalty even if you owe nothing.

Every Self Assessment date for the 2025/26 tax year

The tax year being reported ran from 6 April 2025 to 5 April 2026. These are the dates that apply to it.

Date	What is due	Status
5 October 2026	Register for Self Assessment if this is your first year	Passed
31 October 2026	Paper return must reach HMRC	Passed
30 December 2026	File online to have tax under £3,000 collected through your PAYE code	Next
31 January 2027	Online return, balancing payment, and first payment on account for 2026/27	Main deadline
31 July 2027	Second payment on account for 2026/27	Later

Nearly everyone files online now, so 31 January is the date that matters. The paper deadline catches people out because it is three months earlier and there is no way to switch back to paper once it has gone.

What happens if you miss 31 January

The first penalty is automatic and is not linked to how much tax you owe. People who owe nothing, or who have already paid, still get it.

• The day after the deadline: £100, regardless of whether any tax is due.
• Three months late: £10 for each additional day, up to 90 days, so a maximum of £900 on top.
• Six months late: a further £300, or 5 percent of the tax outstanding if that is higher.
• Twelve months late: the same again.

Late payment is penalised separately from late filing. There are further charges at 30 days, six months and twelve months after the payment was due, and interest runs daily on anything unpaid from 1 February. A return that is twelve months late with tax still outstanding can comfortably pass £1,600 in penalties before the interest is counted.

You missed the 5 October registration deadline

This is the most common problem in October, and it is more fixable than it looks. The penalty for registering late is calculated on the tax you owe, and it can be reduced to nothing if everything due is paid by 31 January 2027.

The practical risk is different. Registering is not instant, because HMRC issues a Unique Taxpayer Reference by post and that typically takes around ten working days. You cannot file without it. Someone who registers in mid January has a real chance of missing the filing deadline as well, and then both penalties apply. If you have not registered, that is this week's job rather than January's.

Do payments on account apply to you?

If your last Self Assessment bill was more than £1,000, and less than 80 percent of your tax was collected at source, HMRC asks for the next year's tax in two instalments. Each one is half of last year's bill.

This is why a first Self Assessment bill often feels like a shock. On 31 January you can be paying the balance for the year just ended and the first instalment towards the year you are currently in, so the cash leaving your account is around 150 percent of the tax you were expecting. If your income has fallen, you can ask HMRC to reduce the payments on account, though you will be charged interest if you reduce them too far.

Does Making Tax Digital change this year's return?

Not the one due in January. Making Tax Digital for Income Tax began on 6 April 2026 for sole traders and landlords with qualifying income over £50,000. That is the 2026/27 tax year, which you are living through now.

The return due by 31 January 2027 covers 2025/26 and is filed exactly as before. The distinction matters because the two things run in parallel: you may be sending quarterly updates for the current year at the same time as finalising last year's return under the old system. If you are already VAT registered the quarterly rhythm will feel familiar, and the same digital record keeping rules that apply to MTD for VAT now apply to income too.

Frequently asked questions

When is the Self Assessment deadline?

Midnight on 31 January 2027 for online returns covering the 2025/26 tax year, and midnight on 31 October 2026 (now passed) for paper returns. Registration for that year closed on 5 October 2026.

What happens if I miss the 31 January deadline?

An automatic £100 penalty applies immediately, even with no tax owing. Daily penalties of £10 start after three months, and there are further charges at six and twelve months. Late payment penalties and daily interest are charged on top.

I missed the 5 October registration deadline. What should I do?

Register now. The late registration penalty is based on the tax owed and can be removed if you pay everything by 31 January. The bigger risk is the ten working days HMRC takes to post your Unique Taxpayer Reference, without which you cannot file at all.

When should I submit my Self Assessment tax return?

Filing early does not mean paying early. You still pay on 31 January, but you know the figure months ahead. File by 30 December 2026 and, if you owe under £3,000 and already pay tax through PAYE, HMRC can collect it through next year's tax code instead of in one payment.

Can I still file if I have lost my UTR or Government Gateway login?

Yes, but not quickly. Both can be recovered from HMRC, and both can involve a code sent by post. In January the helplines are at their busiest. This is the single most common reason an otherwise organised person files late.