You have roughly 100 days from late October to file your 2025/26 Self Assessment tax return and pay what you owe by 31 January 2027. Spread across three months, that is a few hours of work a month instead of a panic in the final week. This countdown plan breaks the job into monthly steps so you file on time, avoid the £100 late filing penalty and know your bill before it lands.
Key takeaways
- Your 2025/26 online return and payment are due by 11:59pm on 31 January 2027.
- Missing the filing deadline means an automatic £100 penalty.
- File online by 30 December 2026 if you want a small bill collected through your tax code.
- January bills can include a first payment on account for 2026/27.
- Sort out your HMRC login early, as access problems take time to fix.
What does the 31 January deadline cover?
The 31 January deadline is the last date to submit an online Self Assessment return for the tax year that ended the previous April, and to pay the tax due. For the 2025/26 tax year, which ran from 6 April 2025 to 5 April 2026, GOV.UK's Self Assessment deadlines page confirms the online return and payment are both due by 11:59pm on 31 January 2027. The paper deadline of 31 October 2026 has already passed, so filing online is now the route for most people.
The 100-day countdown plan
Late October to November: access and records
- Check you can log in. Sign in to your HMRC online account and confirm you can see your Self Assessment. If you need a new activation code or have lost your details, start now, because codes are sent by post.
- Find your UTR. Your 10-digit Unique Taxpayer Reference is on previous HMRC letters and in your online account.
- Gather income records. Use our Self Assessment documents checklist for P60s, P11Ds, bank interest, rental statements and self-employed records.
December: figures and an early estimate
- Total your income and expenses. For self-employment, add up income and allowable expenses for 6 April 2025 to 5 April 2026.
- Draft the return. Enter figures online; you can save and come back without submitting.
- Decide about coding out. If you are employed or get a pension and owe under £3,000, filing online by 30 December 2026 may let HMRC collect it through your tax code; see our guide to paying through your tax code.
January: submit and pay
- Check and submit. Review the calculation, submit, and save the confirmation and submission reference.
- Pay in good time. GOV.UK's pay your Self Assessment bill page lists payment methods and how long each takes to clear.
- Note 31 July 2027. If you have payments on account, the second one for 2026/27 is due then.
Filing early versus filing at the deadline
| File by mid-December | File in the last week of January | |
|---|---|---|
| Know your bill | Weeks in advance | Days before payment is due |
| Coding out option | Available if filed online by 30 December and eligible | No longer available |
| Time to fix login problems | Plenty | Very little |
| Refund timing | Earlier, if one is due | Later |
| Risk of £100 penalty | Low | Higher |
Filing early does not mean paying early. You can submit in December and still pay by 31 January 2027.
Worked example (illustrative example)
Illustrative example only, not a real person. Alex is employed and also runs a weekend photography business. Alex registered for Self Assessment in 2025, so this is the second return.
In late October, Alex logs in and finds the password reset needs a new code by post, which arrives in November. In November, Alex downloads the P60 and totals photography income of £9,400 and expenses of £2,100 for 2025/26. In early December, Alex drafts the return. The calculation shows a balance due, and because Alex's last bill was over the payments on account limit, the January payment includes a first payment on account for 2026/27. Alex submits on 12 December, sets the money aside and pays on 20 January 2027. If Alex had started on 28 January, the login problem alone would have made the return late.
Common mistakes
- Leaving login checks until January. Replacement codes come by post and can take days to arrive.
- Forgetting payments on account. See our guide to payments on account so the January total is not a surprise.
- Missing other income. Bank interest, dividends and rental income all need to be included where they apply.
- Assuming no tax means no return. If HMRC asked you to file, the £100 penalty applies even when nothing is owed.
- Paying by a slow method on the last day. Some payment methods take several working days to reach HMRC.
If you are worried about penalties, GOV.UK's Self Assessment penalties page explains the scale, and our guide to late filing penalties covers appeals. If you cannot pay in full, see GOV.UK's page on difficulties paying HMRC.
How we can help
Our personal tax service starts from £180 per year on a fixed fee. Send us your records in November and we will prepare and file your return well before the deadline and tell you exactly what to pay. See our personal tax service, check our pricing, or contact us to start your countdown.
Frequently Asked Questions
What is the deadline for my 2025/26 online tax return?
GOV.UK says you must submit your 2025/26 online tax return by 11:59pm on 31 January 2027, and pay the tax you owe by the same time. If you registered for Self Assessment after 5 October 2026, HMRC will give you a filing deadline three months from the date of its letter or email, but the payment date stays 31 January 2027.
What happens if I file one day late?
You get a £100 late filing penalty, even if you have no tax to pay or you pay on time. Further penalties can follow if the return is three, six or twelve months late. Interest is also charged on any tax paid late. GOV.UK's penalties page sets out the current scale and how to appeal if you had a reasonable excuse.
I missed the 5 October registration deadline. What should I do now?
Register as soon as possible. Registration can take time because HMRC sends your Unique Taxpayer Reference by post. Once registered, HMRC will tell you your filing deadline. The tax itself is still due by 31 January 2027, so work out what you owe and pay on time even if your filing deadline is later.
Why is my January bill bigger than I expected?
In January you may pay the balance for 2025/26 plus your first payment on account for 2026/27. Payments on account are advance payments, each normally half of your previous year's tax bill, and they apply if your last bill was over a set limit. That combination can make a first January bill much bigger than the tax for a single year.
Can I pay my tax bill in instalments?
If you cannot pay in full, you may be able to set up a payment plan with HMRC, sometimes called Time to Pay. For smaller Self Assessment debts this can often be done online. Interest still runs on the unpaid amount, so contact HMRC before the deadline and pay what you can. GOV.UK explains the options.
Related reading
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Schedule a consultation →Written by the Berber Accounts & Tax team, 124 City Road, London EC1V 2NX, United Kingdom.
Last reviewed: 23 October 2026.
This article is general information, not personal tax advice. Speak to a qualified accountant about your own circumstances before acting on it.