Self Assessment deadlines for 2026 and 2027

If you need to send a Self Assessment return for the last tax year, the dates that matter are set by HMRC, not by a software company and not by this website. The last tax year started on 6 April 2025 and ended on 5 April 2026. That is the year you are filing now. The following notes restate the official deadlines page in our own words, with the dates that page currently publishes for this filing season.

The dates HMRC has published

HMRC must receive your tax return and any money you owe by the deadline that applies to the way you file. Missing a deadline can lead to a penalty, which is why it is worth putting the dates in a calendar now rather than waiting until late January.

You must tell HMRC by 5 October if you need to complete a return for the previous year and you have either not sent a return before, or you registered before but did not need to send a return for 2024/25. You can tell HMRC by registering for Self Assessment. If you register after 5 October 2026, HMRC will send a letter or email with a different deadline to send the return — three months from the date on that letter or email — but you must still pay the tax you owe by 23:59 on 31 January 2027 or you will get a penalty.

For a paper tax return, HMRC must have received it by 23:59 on 31 October 2026. That date has already passed. If you still need to file and you missed paper, switch to the online service and send the return as soon as you can; late-filing charges are already in play once a deadline has gone by, and waiting longer can add daily amounts later in the schedule.

For an online return, you must submit it by 23:59 on 31 January 2027 or you will get a late-filing penalty. You may submit any time on or after 6 April 2026 up to that deadline. If you want to pay the bill through your tax code, you must submit the online return by 23:59 on 30 December 2026. Miss that earlier date and you will have to pay another way. The tax itself, for most people, is also due by 23:59 on 31 January 2027. There is a second payment date of 31 July if you make payments on account towards the next bill.

Trustees of a registered pension scheme and non-resident companies have a paper deadline of 31 January 2027 and cannot send that return online. Partnerships with a company as a partner and an accounting date between 1 February and 5 April have different online and paper windows measured from the accounting date. Check the official deadlines page if that is your situation; this guide is written for the ordinary individual return.

Why 30 December is easy to overlook

The January date is the one most people remember. The 30 December date is narrower and easier to forget, especially if you are away over the holidays. It only helps if you want the bill collected through a tax code, which is a method HMRC offers in some cases rather than a requirement. If you miss 30 December, you can still file online up to 31 January, but you will need another payment method — bank transfer, card, or Direct Debit set up in time, according to the options HMRC shows when you pay.

Submitting in December also gives you a short window to fix mistakes before the January payment date. You can sign in again, check the tax calculation and, if something looks wrong, amend the return through the official service. Leaving the entire job until the evening of 31 January is how people run into identity checks, lost Unique Taxpayer References, or a service that is simply busy.

If you do not yet know your profit

The official deadlines page is clear that if you do not know your profit for the whole tax year, you still need to send a return. HMRC publishes separate help on sending a return when the profit figure is not yet final. Do not treat an incomplete set of records as a reason to ignore the date. File on time with the best figures you can support, and keep the records that sit behind them: invoices, bank statements, mileage logs and receipts. If a figure later changes, the official service explains how amendments work.

Payments on account sit on a second clock

Filing and paying the 2025/26 bill by 31 January 2027 is only part of the cash-flow picture if payments on account apply to you. Those instalments are payments towards the next bill, each usually half of last year’s relevant tax, due by midnight on 31 January and 31 July. The January payment can therefore be a balancing amount for last year plus the first instalment towards 2026/27. The second instalment that belongs with that new year is due on 31 July 2027. Our payments on account calculator walks through the official £1,000 and 80% tests; the payments on account guide explains the idea in longer form.

What happens if a date is missed

Late filing and late payment have separate official penalty lists, and interest can be charged on unpaid tax as well. The initial late-filing penalty is £100, with daily penalties after three months and further percentage charges after six and twelve months. Late-payment penalties are 5% of tax unpaid at 30 days, six months and twelve months. Those rules are set out in our penalties guide and in the penalty calculator. The right response to a missed date is still to send the return and pay as soon as you can, because some charges keep growing with time.

If you needed to register and you left it until after 5 October, a “failure to notify” penalty can also arise when tax is still unpaid on 31 January. That is a different official schedule, described in HMRC factsheet CC/FS11, and it is not a reason to delay filing further.

How to put the dates to use

Start with HMRC’s own question: do you need to send a return at all? The official “who must send a tax return” page and the “check if you need a tax return” tool are the places to answer that. If HMRC has already written to you asking for a return, you must send one by the deadline on the letter even if you think nothing is due. If you do need to file, register or reactivate in time to receive a Unique Taxpayer Reference, then file online for free on GOV.UK. You do not have to complete the return in one sitting; the official service lets you save and come back.

AssessTally’s tax calculator can give a planning figure for Income Tax and Class 4 National Insurance so you can set money aside before 31 January. It is an independent estimate, not HMRC’s calculation. NewDeduct and Year-End Moves, elsewhere on dollarfinch.com, are US federal tax tools and do not apply to a UK Self Assessment return.

The only dates that count are the ones on GOV.UK. If HMRC later updates a page, the official wording wins over this guide.