Self Assessment Deadlines 2025/26: The Full HMRC Calendar

When are the Self Assessment deadlines for the 2025/26 tax year? Five dates matter. You register by 5 October 2026, file a paper return by 31 October 2026 or an online one by 31 January 2027, pay what you owe by 31 January 2027, and make a second payment on account by 31 July 2027. From today, 7 August 2026, the next of those is registration on 5 October, and every date after it carries a penalty of its own if you slip past it.

This guide lays out the full calendar for the return you are filing now, then puts a number on each missed deadline: the £100 that lands the day you are late, the daily charges that follow, and the 7.75% interest underneath it all.

The Self Assessment deadlines for the 2025/26 tax year

The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. If you had untaxed income in that window, these are the dates HMRC holds you to. Every one is quoted from HMRC's Self Assessment deadlines guidance.

The load-bearing date is 31 January 2027. It is the online filing deadline and the payment deadline at once, so a single missed 31 January triggers two separate penalty tracks, one for the return and one for the money. They accrue on different clocks, so this guide treats them separately.

Who has to file, and who has to register by 5 October

You need a return if, in 2025/26, you were self-employed with gross trading income above £1,000, a partner in a business, or received untaxed income HMRC could not collect through PAYE (rental profit, dividends above your allowance, foreign income, some capital gains). The £1,000 trading allowance is the line for a side hustle: below it there is nothing to report, above it a return is due.

Registration is the step people forget, because it has the earliest deadline and the quietest one. HMRC's registration guidance is direct: "You must tell HM Revenue and Customs (HMRC) by 5 October 2026 if you need to complete a tax return for the previous tax year." Miss it and "you could get a penalty", because a late registration is a failure to notify, geared to the tax you owed.

If you filed last year you do not register again; first-timers do, as does anyone who dropped out and now has income to report. Our walkthrough of registering as a sole trader covers what the sign-up asks for and how long the activation code takes, which is why 5 October is not a date to leave to the last week.

Payments on account: why January asks for more than one year's tax

The 31 January bill catches people out because it is rarely just the tax for the year you filed. HMRC's payments on account system makes you pay towards the following year in advance, in two instalments due 31 January and 31 July. You make them unless "the amount of tax you owed last year was less than £1,000" or "last year you paid more than 80% of the tax you owed outside of Self Assessment", and each is "usually half of the tax you owed the previous year".

So your 31 January 2027 payment is the balancing payment for 2025/26 plus the first instalment towards 2026/27. In a first year of self-employment, with no prior instalment to reduce the balance, that combination is what turns an expected bill into one half as large again. The 31 July payment clears the rest of the estimate. Neither is a new tax: both are credited against what you finally owe, and HMRC refunds any overpayment.

What each missed deadline costs

Late filing and late payment are penalised on two independent timelines, and interest runs on top of the second. All the figures below come from HMRC's Self Assessment penalties guidance.

The £100 is the one to notice: it lands the day after 31 January whether or not you owe anything, so a nil return filed a day late still costs £100. On top of every late payment charge, HMRC adds interest. The late payment interest rate is 7.75% from 9 January 2026, set at the Bank of England base rate plus 4% since 6 April 2025, and it accrues daily from 1 February until you pay.

Take a return filed and paid a full year late on a £2,000 bill. The filing penalties stack to £100 plus £900 plus £300 plus £300, which is £1,600. The late payment penalties are 5% three times over, £300 in total. Interest at 7.75% on £2,000 across the year adds roughly £155. That is about £2,055 in penalties and interest on a £2,000 tax bill, and the return was no harder to file in February than it would have been in January.

If you cannot file or pay on time, HMRC can cancel a penalty where you have a reasonable excuse, and a bill you cannot meet can be spread through a Time to Pay arrangement. Neither is automatic: you have to ask, and the interest still runs.

What changes under Making Tax Digital from April 2026

The 31 January and 31 July dates stay, but the way you report is changing for the largest sole traders and landlords first. Under Making Tax Digital for Income Tax, quarterly updates through compatible software replace the once-a-year keying of figures.

The rollout is staged by qualifying income: from 6 April 2026 above £50,000, from April 2027 above £30,000, and from April 2028 above £20,000. Below £20,000 you stay on the annual return for now. If your income clears £50,000 you are already in the first phase, so 2026/27 is the year to get your records into digital shape. Our guides to Making Tax Digital for Income Tax and the penalties under MTD cover the points-based regime that applies once you sign up.

How to be ready before each date

Every deadline rewards the same habit: records that already exist when the date arrives. The January scramble is rarely about the form, which takes an evening. It is about rebuilding a year of figures from bank statements and a bag of receipts, and that is the part you can front-load.

Three things carry the most weight when you file:

1. A running total of income and expenses. This is the figure the return asks for, and it tells you whether you owe enough to trigger payments on account. Keeping it current makes 31 January a transcription job, not an investigation.
2. Every receipt behind a claimed expense. HMRC can ask you to prove any figure for up to five years after the 31 January deadline, per its record-keeping rules. Thermal receipts fade well inside that window, so a photo taken on the day is the version that survives.
3. A note of what each cost was for. A bank line reading "£240" is not a deduction until you can say it was an allowable expense, and capturing that at the time beats guessing months later.

This is the routine SparkReceipt is built around. Photograph a receipt and the AI receipt scanner pulls out the vendor, date, total and VAT, so the record exists before the paper fades. Connect Gmail or Outlook and emailed receipts are captured without forwarding. When the return is due, the expense tracker gives you one categorised total to enter and the images to back it up if HMRC asks.

Frequently asked questions

When is the Self Assessment deadline for 2025/26?

The online filing and payment deadline for the 2025/26 tax year is 11:59pm on 31 January 2027, per gov.uk. A paper return is due earlier, by 31 October 2026, and you must have registered by 5 October 2026 if you are new to Self Assessment.

What is the penalty for filing a day late?

A fixed £100, charged the day after the deadline, even if you have no tax to pay or are due a refund. HMRC's penalties guidance adds £10 a day once the return is three months late, up to £900, then tax-geared penalties at six and twelve months.

Do I have to make payments on account?

Only if your last Self Assessment bill was £1,000 or more and less than 80% of your tax was collected at source. If so, HMRC asks for two instalments, each usually half of the previous year's tax, on 31 January and 31 July.

What if I registered late for Self Assessment?

File and pay everything by 31 January and you often avoid a separate failure-to-notify penalty, because it is geared to tax unpaid after the due date. Registering late is still a risk worth avoiding, since the activation code can take a week or more and 31 January does not move for you.

Key takeaways

• Five dates govern the 2025/26 return: register by 5 October 2026, paper file by 31 October 2026, file online and pay the balance plus the first payment on account by 31 January 2027, and make the second by 31 July 2027.
• The next deadline from today is registration on 5 October 2026. It has the earliest date and the quietest penalty, and the activation code takes time to arrive.
• 31 January is two deadlines in one, so missing it starts a late filing penalty and a late payment penalty on separate clocks.
• A £100 fixed penalty lands the day you are late even if you owe nothing, and a year-late £2,000 bill can attract roughly £2,055 in penalties and interest.
• Late payment interest is 7.75% from 9 January 2026 and accrues daily, so paying part of a bill on time still cuts the running cost.
• Making Tax Digital for Income Tax starts on 6 April 2026 above £50,000, April 2027 above £30,000, and April 2028 above £20,000, but the payment dates stay the same.

Get Started with SparkReceipt and keep every receipt and expense current, so each Self Assessment deadline is a figure you already have rather than a January reconstruction.