Now that the 31 July payment on account has been and gone, the next Self Assessment date in the calendar is 5 October. It is comfortably the least famous deadline of the tax year, and it catches more people than any other, because it applies to those who have never dealt with Self Assessment before and so have no reason to be looking for it.

What the deadline actually is

If you need to send a tax return for the 2025 to 2026 tax year (6 April 2025 to 5 April 2026) and you have never sent one before, you have to tell HMRC by 5 October 2026. The same applies if you have filed in the past but did not need to file for 2024 to 2025, because HMRC will have taken you back out of the system.

Registering is not the same as filing. It is simply telling HMRC that you have income to declare, so it can issue your Unique Taxpayer Reference and a notice to file. The return itself, and the tax, are not due until 31 January 2027.

Who needs to register

The common ones we see:

  • You worked for yourself and took more than £1,000 in gross income, before deducting any of your costs. That figure is turnover, not profit, so a small side business that barely broke even can still cross it.
  • You started letting out a property. Rental income is not taxed at source, so it reaches HMRC through a return.
  • You became a partner in a partnership.
  • You had untaxed income such as dividends, savings interest or foreign income that your tax code does not already deal with.
  • You owed Capital Gains Tax, for example on a second property or on shares.
  • You had to pay the High Income Child Benefit Charge and are not paying it through your tax code.

Being a company director is not, on its own, a reason to register. What usually brings a director into Self Assessment is the money coming out of the company, not the job title.

The £1,000 figure, and the one that is coming

The £1,000 trading allowance is the current line for self-employment. Below it, you generally have nothing to report. Above it, you do, even if there is no profit left once expenses come off.

The government has announced that this reporting threshold will rise to £3,000 of gross trading income, with a simpler digital service for people underneath it. That change has not happened yet and no start date has been confirmed, so for the 2025 to 2026 tax year the £1,000 figure is still the one that counts. Do not plan around the higher number until it is law.

What happens if you miss 5 October

Missing this date does not trigger an automatic fine in the way a late tax return does. It falls under what HMRC calls a failure to notify, and any penalty is worked out as a percentage of the tax you owe rather than as a flat amount.

If it was a genuine oversight and you come forward yourself within 12 months of the tax being due, the penalty range starts at nothing. Wait to be found instead, and it starts at 10 per cent and climbs from there. Where there is a reasonable excuse, HMRC charges no penalty at all.

So the practical position is straightforward. If you realise you should have registered, whether for this year or an earlier one, register straight away and pay what you owe by the January deadline rather than keeping quiet and hoping. In most honest cases that combination costs nothing.

One more reason to get in on time

Your 2025 to 2026 return is also the one HMRC uses to decide whether Making Tax Digital for Income Tax applies to you from April 2027, when the threshold drops to £30,000 of gross income from self-employment and property. Register late and file late, and the first you hear about a quarterly reporting duty could be a letter telling you it has already started. Our guide to Making Tax Digital for Income Tax sets out the full timetable.

Let us take it off your desk

We register clients for Self Assessment, deal with HMRC on your behalf, prepare the return early, and tell you what you owe months before it is due. Our Sole Trader service is £62.50 per month, fixed, with no surprise bills for picking up the phone.

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