The Self Assessment deadline before the deadline

If you need to complete a Self Assessment for the 2025/26 tax year and you have not filed one before, you need to tell HMRC by 5 October 2026.

That is not the deadline for filing your return, and it is not the deadline for paying anything. It is the point at which you register, so HMRC knows to expect a return from you at all.

It is the step everything else depends on, and it is the one people miss.

Does this apply to you?

It usually does if something changed for you during the 2025/26 tax year and you have not completed a return before. Common reasons include:

• You started working for yourself, full time or alongside a job
• You became a partner in a partnership
• You started receiving rental income
• You had income from savings, dividends or investments that is not taxed at source
• You sold something that produces a capital gain

That list is not exhaustive, and the rules turn on individual circumstances rather than on job titles. If you are reading this and thinking “possibly”, that is a good reason to ask rather than assume.

What happens if you miss it

HMRC can charge a penalty for registering late.

It is an avoidable one, which is what makes it frustrating. The registration itself is not difficult or time consuming. It is simply a job that sits quietly in the background while you get on with running a business, until it is suddenly late.

It is a short job

Registering is quick, particularly compared with everything that follows it.

If Willis Cooper looks after your tax, we can deal with it for you. If you would rather do it yourself, we can tell you what you need before you start, so you are not working it out as you go.

With the deadline falling on Monday, the useful thing is to sort it in the next day or two rather than leaving it to the last moment.

Already file a return? October is still a good month

If you are already registered, 5 October is not your date. Yours is 31 January 2027.

But there is still a reason not to leave it.

Sending us your records now means we can prepare your return and tell you what your tax bill will be, months before you have to pay it. And filing early does not bring the payment date forward. You would still pay in January. You would simply know the number in October instead of guessing until Christmas.

The same works in reverse. If you have overpaid, perhaps through payments on account based on a stronger previous year, filing early means the repayment comes back to you sooner.

It also leaves room for the awkward bits. A missing statement or an unanswered question is a small job in October. In late January it is a problem.

What to do now

If 2025/26 was your first year of self employment, rental income or anything else that brings you into Self Assessment, check whether you need to register before 5 October.

If you are already in the system, dig out your 2025/26 records and send them over.

If you are not sure which of those applies to you, that is exactly the sort of question the team would rather answer now than in January.

If you want to read more about our tax services, payroll support or cloud accounting.