Self Assessment 2026-27: the 5 October deadline that arrives first
Anyone filing a Self Assessment tax return for the first time must tell HMRC by 5 October 2026, GOV.UK says — the earliest of several deadlines that run through to next summer.
Anyone who needs to complete a Self Assessment tax return for the 2025-to-2026 tax year for the first time — or who registered before but did not need to file for 2024-to-2025 — must tell HMRC by 5 October 2026, according to GOV.UK’s guidance on Self Assessment deadlines. That tax year ran from 6 April 2025 to 5 April 2026.
GOV.UK says the way to “tell” HMRC is to register for Self Assessment. Registering late does not cancel the requirement. HMRC instead writes to set a new return deadline, three months from the date of that letter — though the tax owed must still be paid on time regardless of when registration happens.
| Deadline day | GOV.UK’s description |
|---|---|
| 5 October 2026 | Tell HMRC you need to file, if this is your first return or you didn’t need one last year |
| 30 December 2026 | Online return deadline if you want tax collected through your tax code |
| 31 October 2026 | Paper tax return received by HMRC |
| 31 January 2027 | Online tax return received by HMRC, and the tax bill paid |
| 31 July 2027 | Second ‘payments on account’ instalment, for those who make them |
What happens if I register late?
Registering after 5 October 2026 can still bring a penalty, GOV.UK’s guidance says. HMRC’s own letter or email then names a return deadline three months on from that date. The payment deadline for the tax owed does not move with it.
Paper or online — does it change the date?
Yes. GOV.UK sets two separate filing deadlines depending on the format. A paper tax return has to reach HMRC by 31 October 2026. An online return has three months longer, up to 31 January 2027. Both can be filed any time from 6 April 2026 onwards, GOV.UK says, so early filers are not penalised for submitting sooner.
What is the 30 December date about?
That earlier online deadline only applies to taxpayers who want HMRC to collect what they owe automatically through their tax code, rather than paying it as a lump sum. Anyone who misses the 30 December 2026 cut-off loses that option, GOV.UK says, and has to pay another way. The return can still be filed later, up to 31 January 2027, just not through the tax code.
Who has different deadlines?
Trustees of a registered pension scheme, and non-resident companies, must send a paper return by 31 January 2027 and cannot file online, GOV.UK says. A different rule covers some partnerships with a limited company as a partner, giving them 12 months from their own accounting date for an online return, or 9 months for a paper one.
Missing any of these dates brings an automatic late-filing penalty on top of interest on unpaid tax, GOV.UK’s guidance says. A late registration is penalised separately from a late return.