UK Self Assessment deadlines, 2025-26

Self Assessment is the UK tax return system for income that PAYE does not cover, and its calendar ruins more Januaries than any other deadline in money. The dates are fixed, published, and unforgiving — here is the whole map for the 2025-26 tax year, with the dates the penalties run on.

The four dates that matter

The 2025-26 tax year covers income from 6 April 2025 to 5 April 2026. For it, the UK deadlines run: 5 October 2026 to register if you have never filed before · 31 October 2026 for paper returns · 30 December 2026 if you want HMRC to collect what you owe through your PAYE tax code (only for eligible amounts under £3,000) · and the one everyone means by “the deadline”: 11:59pm on 31 January 2027 for online filing and for paying the tax due, including the first payment on account for 2026-27. The second payment on account for 2026-27 follows on 31 July 2027.

What happens if the date passes

A £100 penalty applies automatically the moment you miss the filing deadline — even if you owe nothing. Daily penalties and further charges stack after three and six months, and late payment adds interest plus a percentage surcharge. This is the part people get wrong twice: the filing penalty and the payment penalty are separate, and zero tax owed does not mean zero penalty. File the return; pay what is due; the two clocks stop. Keep one printed copy of the dates; the GOV.UK page is the authority, and it is also the page to check the week before you file, because small date changes happen at fiscal events.

Who actually needs to file

This is a UK rule page, so the jurisdiction matters: if you are taxed in the UK, the usual triggers are self-employment income over the trading allowance, untaxed income (rent, dividends, foreign income), a high-income child benefit charge, or a notice from HMRC — which legally obliges you even when no tax is due. If your tax affairs are simple and fully PAYE, you may not be in Self Assessment at all; check before you assume either way. The GOV.UK deadlines page is the authority to re-read before every January.

The honest workflow

Three habits erase most of the pain. Do the return in April, not January — the numbers are the same and the helpline is not. Set the payment aside monthly as you earn, because the bill is never a surprise to someone who saved for it. If January is genuinely impossible, file anyway and talk to HMRC about a payment plan before the surcharges land; a filed return with a payment arrangement is a far cheaper outcome than silence. And treat 31 January as a hard stop, not a target: the online portal is slowest on deadline day, and a slow portal is still a late return. For the wider calendar — what else lands in the same months — the house event calendar carries the tax dates alongside everything else the desks cover.

Sources and further reading

Links were reviewed 2026-09-29. Regulatory permissions, firm status and product terms can change; use the current official register before acting.

1. GOV.UK — Self Assessment: deadlines
2. GOV.UK — Self Assessment: who must send a return

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