Important: FilingFriend provides general informational guidance about UK filing requirements. It does not provide tax, accounting, or legal advice. Always confirm requirements with HMRC or Companies House.
Who usually needs to pay attention to the 5 October deadline
The registration deadline matters most if you are new to Self Assessment and have started self-employment, received untaxed income, or begun receiving rental income that means you need to file.
The date is tied to the end of the tax year, not the date you started trading. If you first needed to file for the tax year ending 5 April 2026, the registration deadline is 5 October 2026.
What registration actually does
Registering tells HMRC that you need to be brought into Self Assessment. It is separate from filing the tax return itself.
After registration, HMRC can issue your Unique Taxpayer Reference if you do not already have one and set up the account details you need for filing online.
Why it is worth doing early
Leaving registration until the last moment creates avoidable risk. You may need time to receive account details, complete identity checks, and gather records before the January filing deadline arrives.
If you know you will need to file, early registration is usually the safer approach.
Key deadlines
| Action | Deadline | Why it matters |
|---|---|---|
| Tax year ends | 5 April each year | The registration deadline is counted from the end of the relevant tax year. |
| Tell HMRC you need Self Assessment | 5 October after the tax year ends | For example, for the tax year ending 5 April 2026, the deadline is 5 October 2026. |
| Online tax return and balancing payment | 31 January after the tax year ends | Registration does not replace the filing deadline. |
Official references
FAQ
Do I register on the same day I start trading?
Not necessarily. HMRC's deadline is 5 October after the end of the tax year in which you started, but registering earlier is usually easier.
Is registration enough on its own?
No. You still need to file your return and pay any tax due by the relevant Self Assessment deadlines.
Next step
Keep the main dates visible
Use the FilingFriend calendar as a quick reminder layer, then return to this guide when you need the fuller explanation or official source links.