Self Assessment for the 2025/26 tax year has two return deadlines and two payment deadlines. The one that matters to most people is 31 January 2027 — file your online return and pay any tax you owe by then, or HMRC starts charging penalties and interest the next day.
The 2025/26 Self Assessment calendar
| Date | What's due | Applies to |
|---|---|---|
| 5 April 2026 | End of the 2025/26 tax year | Everyone |
| 5 October 2026 | Deadline to register for Self Assessment if this is your first return, or you stopped filing and need to start again | First-time filers, returning filers |
| 31 October 2026, 11:59pm | Paper tax return deadline | Anyone filing on paper |
| 30 December 2026, 11:59pm | Deadline to submit online if you want HMRC to collect tax you owe (under the coding-out threshold) through your PAYE tax code instead of a lump sum | Employees who also file Self Assessment |
| 31 January 2027, 11:59pm | Online tax return deadline and balancing payment due | Everyone filing online |
| 31 July 2027 | Second payment on account due | Anyone HMRC has asked to make payments on account |
Every date above is HMRC's own wording, from its Self Assessment deadlines page and its registering for Self Assessment guidance. Note that these are the deadlines for the 2025/26 tax year (6 April 2025 to 5 April 2026) — the return you'd be filing in the 2026/27 season. Each tax year has its own version of this calendar, so don't assume this year's dates carry over unchanged to the next.
Registration: 5 October 2026
If you've never filed a Self Assessment return before — you started freelancing, began renting out a property, or your income moved above a reporting threshold during 2025/26 — you must tell HMRC by 5 October 2026. Miss this and you can still be fined even if you go on to file and pay on time, because the registration deadline is separate from the filing deadline.
Registration is done online at gov.uk/register-for-self-assessment. HMRC then posts you a Unique Taxpayer Reference (UTR) — usually within about 15 working days, longer if you're overseas. You need that UTR before you can file, so don't leave registration until the last week of a busy October. If you've registered before but didn't need to file last year, you may need to reactivate your account rather than register from scratch — see our how to find your UTR number guide if you've lost track of an existing UTR.
Filing: 31 October (paper) or 31 January (online)
Almost everyone files online now, which pushes the deadline three months later than the paper deadline — 31 January 2027 for online versus 31 October 2026 for paper. HMRC's own guidance is explicit that a paper return received even one day after 31 October counts as late, with no allowance for the fact that the online deadline is later.
There's a lesser-known middle date too: 30 December 2026. If you're employed (or receive a pension) and also file Self Assessment, you can ask HMRC to collect what you owe automatically through your tax code across the following tax year, instead of paying it in one go. To use this option your return has to reach HMRC by 30 December, not 31 January — miss that earlier date and you fall back to paying the balance directly by 31 January.
Payment: 31 January and 31 July
The 31 January deadline covers two different amounts that often get confused:
- The balancing payment — the tax you actually owe for 2025/26, once your return has been calculated.
- The first payment on account for 2026/27 — an advance instalment towards next year's bill. HMRC requires payments on account unless last year's tax bill was under £1,000, or you already paid more than 80% of what you owed outside Self Assessment — see gov.uk on payments on account.
If HMRC has set payments on account for you, the second payment on account — the other half of that advance instalment — is due separately on 31 July 2027. Both instalments are based on last year's bill (see gov.uk on payments on account for how the amount is worked out), not a fresh estimate of the current year.
If you can't pay by 31 January
Filing on time and paying on time are two separate obligations, and missing one doesn't excuse the other — HMRC can charge a late-filing penalty even if you can't pay, and interest on unpaid tax regardless of whether you filed on time. If you know in advance that you won't be able to pay the full balance by 31 January, HMRC's guidance on help if you cannot pay your tax bill points to a payment plan (Time to Pay) that spreads the amount over instalments — it's worth setting this up before the deadline rather than after, since a plan agreed in advance can reduce the penalties that follow a missed payment.
The one thing that doesn't help is delaying the return itself while you sort out how to pay. File on time regardless — the return and the payment are assessed against separate deadlines and separate penalty regimes, covered in full in our self assessment late filing penalty guide.
A practical countdown
- April–September: gather records — bank statements, invoices, P60/P45s, dividend vouchers, rental income and expenses. Register now if this is your first return; don't wait for the 5 October cutoff.
- October: file on paper by 31 October if you're one of the small minority who still does (or if you want a paper acknowledgment for a specific reason). Otherwise, keep going online.
- November–December: file early if you want the 30 December coding-out option, or simply to avoid the January rush and to know your bill with enough notice to budget for it.
- January: file and pay by 31 January regardless of route. This is also when the first payment on account for the following year falls due, so budget for both amounts, not just the balancing payment.
- July: pay the second payment on account by 31 July if HMRC has asked for one.
If any of these dates has already passed and you haven't filed, go straight to our self assessment late filing penalty guide — the penalty clock starts the day after the missed deadline, so the priority is filing as soon as you can, not waiting for a "better" moment.
How ac-co does this
Once you're signed in, ac-co tracks every date in this calendar against your own filing status — registration, both return deadlines and both payment dates — and tells you which one applies to you rather than showing a generic calendar. It drafts your SA100 from your connected accounts and documents ahead of the January rush, and files directly with HMRC once you approve it, so there's no separate step of printing, posting or manually keying figures into HMRC's own portal.
Related reading
- Self assessment late filing penalty — what happens, and how much, if you miss a date above.
- How to get your SA302 — the tax calculation you'll need once you've filed, e.g. for a mortgage application.
- How to find your UTR number — needed to register and to file.