Registering for Self Assessment and your UTR
You cannot file a tax return without a UTR, and a UTR arrives by post after you register. That sequence is why the registration deadline matters far more than it looks, and why leaving it until January does not work.
Updated 11 September 2026 · Return for the tax year ended 5 April 2026
The Self Assessment register deadline #
Register by 5 October 2026 for the tax year that ended 5 April 2026. The rule is 5 October following the end of the tax year, and it applies if you have never filed before, or if you did not need to file last year.
If you already have a UTR from a previous year you do not register again. A dormant account usually just needs reactivating.
How to register #
HMRC has consolidated this into one online service. You tell it why you need to file and it routes you accordingly, so there is no longer a form number to memorise. Before starting, check that you actually need to file at all, since HMRC also provides a checker for that and a lot of people register unnecessarily.
Self assessment sole trader registration is the most common route through this, and it does two jobs at once: it puts you into Self Assessment and registers you as self-employed for National Insurance. You will need your National Insurance number, your address, and, if self-employed, the date you started trading and what the business does. Registering as self-employed also sets up Class 2 and Class 4 National Insurance, which is a second reason not to skip it.
Who has to register at all is covered in Self Assessment deadlines and payments on account, along with every other date in the cycle.
What a UTR is #
A Unique Taxpayer Reference. Ten digits, no letters, no slash. Issued once and yours for life, even across decades of not filing.
It identifies you. If you also run a limited company, that company has its own separate UTR for Corporation Tax, and the two are not interchangeable. Using the company UTR on a personal return, or the reverse, is a common and time-consuming mistake.
Where to find your UTR number #
- Previous tax returns
- Any Self Assessment letter, statement or payment reminder from HMRC
- Your Personal Tax Account
- The HMRC app
- Your notice to file, if one was issued
The references you will end up holding #
| Reference | Shape | Belongs to |
|---|---|---|
| Self Assessment UTR | 10 digits | You, for life |
| National Insurance number | 2 letters, 6 digits, 1 letter | You, for life |
| Company UTR | 10 digits | Your company, for Corporation Tax |
| Employer PAYE reference | 123/AB456 | Your employer |
| Accounts Office reference | 123PX00123456 | A PAYE scheme, for paying |
The SA302 #
A Self Assessment SA302 is the tax calculation HMRC produces once you have filed. It sets out your income for the year and the tax due on it, and it exists mainly because lenders need proof of income for people who do not have payslips.
Mortgage lenders typically ask for the last two or three years, and almost always want the SA302 together with the tax year overview. The overview is the separate document showing what was charged and what was paid. One without the other is usually sent back.
Both come from your HMRC online account after the return has been filed and processed. If your accountant filed through commercial software, HMRC may not hold a version you can print yourself, and lenders will generally accept the software's own tax calculation instead, provided the tax year overview comes with it.
The practical point: you cannot get an SA302 for a year you have not filed. Anyone applying for a mortgage should file early rather than sitting on the January deadline, because the document only exists once the return is in.
If you registered and nothing arrived #
Chase it before the filing deadline, not after. HMRC's published processing times move, so check the current figure rather than assuming, but the thing not to do is wait quietly and then discover in late January that you still cannot file.
A missing UTR is not a reasonable excuse for filing late if you registered too close to the deadline. It can be one if you registered in good time and HMRC was slow, which is another reason to register early and keep the confirmation.
Self Assessment registration online, and the forms #
Self assessment registration online is the only sensible route now: one service that asks why you need to file and sends you down the right path. The old self assessment registration form route still exists on paper for people who cannot use the online service, but it is slower and it delays the UTR.
The self assessment registration deadline is 5 October 2026, and missing it can itself attract a penalty where tax turns out to be due.
Contacting HMRC about Self Assessment #
Searches for a self assessment HMRC contact number, a self assessment contact number, a self assessment phone number, self assessment general enquiries or the self assessment HMRC address all want a way through to HMRC. Take those details from GOV.UK on the day rather than from a third party: HMRC numbers change, opening hours change, and numbers republished elsewhere are often stale or belong to paid call-forwarding services.
Most of it does not need a phone call. Your Personal Tax Account and the HMRC app show your self assessment UTR number, what you owe, what you have paid, and your filing status. There is an online chat service for simple queries, and agents have a separate self assessment agent line which is not available to taxpayers directly.
For post, the self assessment address is Self Assessment, HM Revenue and Customs, BX9 1AS. BX9 is a special HMRC postcode with no street name, which is correct rather than incomplete.
Self assessment: what can I claim? #
Self assessment what can I claim is the most common question after the deadline itself, and the rule is short: expenses incurred wholly and exclusively for the business.
For the self-employed that covers stock and materials, tools and equipment, business travel and mileage, a proportion of phone and internet, professional fees, insurance, and business premises costs. Self assessment working from home is claimable either through the simplified flat rate by hours worked, or by apportioning actual household costs by rooms and time used.
What is not claimable: ordinary commuting, client entertaining, clothing that is not protective or a uniform, and anything with a private element that cannot be separated out.
Stopping Self Assessment #
Registering is easy to find. Getting out again is not, and people stay in the system for years after they stopped needing to be in it, collecting notices to file and penalties for returns nobody needed.
If your circumstances have changed, tell HMRC. Stopping trading, a rental property sold, a side business wound up, income that has dropped back under the thresholds: none of it reaches HMRC on its own. Until you tell them, the notice to file keeps arriving and the obligation is real.
Two things to know. First, you usually still have to file one final return covering the period up to the date you stopped, so leaving the system is not instant. Second, your UTR is not cancelled or reissued. It stays dormant against your record and comes back to life if you ever need to file again, which is why it is worth writing down somewhere permanent even after you have left.
For the self-employed there is a separate step: telling HMRC you have stopped trading also stops Class 2 National Insurance. Leaving that running is a small charge that quietly continues for years.
Common questions #
When do I have to register for Self Assessment?
By 5 October 2026 for the tax year that ended 5 April 2026. The deadline is 5 October following the end of the tax year, and it applies if you have never filed before or did not need to file last year.
What is a Self Assessment UTR?
A Unique Taxpayer Reference: ten digits, issued once, yours for life. It identifies you to HMRC for Self Assessment and you cannot file a return without it. A company has its own separate UTR for Corporation Tax.
Where do I find my UTR number?
On previous tax returns, on any Self Assessment letter or statement from HMRC, in your Personal Tax Account, and in the HMRC app. It is not printed on a P60 or P45, which are employment documents and carry your employer's PAYE reference instead.
How long does a UTR take to arrive?
HMRC posts it after you register, and it is not instant. Since you cannot file without it, registering close to the 5 October 2026 deadline leaves very little room. Check HMRC's current processing times rather than assuming a number, because they move.
What is an SA302?
The tax calculation HMRC produces from your submitted return, showing your income and the tax due on it. Lenders ask for it as proof of income for the self-employed, usually alongside a tax year overview, and normally for the last two or three years.
Can I get an SA302 if my accountant filed for me?
Yes, but not always from HMRC directly. If the return was filed with commercial software, lenders will often accept the tax calculation printed from that software instead, provided it is accompanied by the tax year overview from your HMRC account.
Do I need to register if I already have a UTR?
No. A UTR is issued once and stays with you. If you have filed before but stopped, the account may simply need reactivating rather than a fresh registration.