If you have just started working as a self-employed associate or locum dentist, one of your first jobs is to tell HMRC. Registering for Self Assessment is how you do that, and there is a firm deadline attached to it. This page covers who has to register, when, exactly how to do it, what changes if you also have a PAYE salary, and what happens once you are in the system. For the detail of preparing and filing the annual return itself, see our dentist Self Assessment filing guide.
Who has to register
You must register for Self Assessment if you have income that is not already taxed at source. For dentists, the most common trigger is becoming self-employed. A UK dental associate is normally self-employed for tax purposes, because the working arrangement (clinical autonomy, your own indemnity, a fee-split or per-UDA payment) supports that status. Your practice pays you gross, with no tax deducted, so the responsibility to declare and pay sits with you.
You will need to register if any of the following apply:
- You have become a self-employed associate. This covers the majority of associates, whether your work is NHS, private or mixed.
- You work as a self-employed locum. Day-rate and percentage locum work paid gross brings you into Self Assessment.
- You have left foundation training and gone self-employed. During dental foundation training you are a salaried employee taxed under PAYE, so you do not register on that basis. The point you move to a self-employed associate role is the point Self Assessment begins.
- You have self-employed income alongside an employed role. Even modest private or sessional income on top of a PAYE post needs declaring.
- You are a practice owner or partner. Sole traders and partners (and members of an LLP) report their share of profit through Self Assessment.
A note on company directors: if you run your dental work through a limited company, the company has its own obligations, and you as a director may or may not need a personal return depending on how you draw income. That is a different question from registering as self-employed, and it is worth taking advice on the structure before you assume either way.
Employed or self-employed: check before you register
Registration follows your employment status, not the type of dentistry you do. Status is determined by the substance of the arrangement, not the label on the contract. The widely used BDA model associate agreement is drafted to support self-employed status and is good evidence, but it does not guarantee it. HMRC weighs factors such as control, personal service and the right to send a substitute, financial risk and how integrated you are into the practice.
In practice almost all associates and locums are self-employed and do need to register. If you are genuinely employed, with tax and National Insurance deducted from your pay through PAYE, you may not need to register at all, unless you have other untaxed income. If you are unsure which side of the line you fall, settle that first, because it decides whether you register and how you are taxed.
The 5 October deadline, and why missing it matters
The deadline is the part dentists most often get wrong. You must tell HMRC that you need to complete a tax return by 5 October following the end of the tax year in which you first became liable. The UK tax year runs from 6 April to 5 April.
So if you started self-employed dental work at any point during the 2025/26 tax year (6 April 2025 to 5 April 2026), your deadline to register is 5 October 2026. The trigger is when you started, not when your first tax bill is due.
| You started self-employed work | Tax year | Register by | First return covers | First payment due |
|---|---|---|---|---|
| Anytime 6 Apr 2025 to 5 Apr 2026 | 2025/26 | 5 October 2026 | 2025/26 | 31 January 2027 |
| Anytime 6 Apr 2026 to 5 Apr 2027 | 2026/27 | 5 October 2027 | 2026/27 | 31 January 2028 |
Why it matters: if you register late and have not paid all the tax due by the following 31 January, HMRC can charge a failure-to-notify penalty. This is not a flat fee. It is calculated as a percentage of the tax that should have been notified (the potential lost revenue), and the percentage depends on your behaviour. An innocent oversight sits at the bottom of the range, a deliberate failure at the top. The penalty is reduced where you come forward yourself before HMRC contacts you (an unprompted disclosure) rather than waiting to be found. There is no penalty where you have a genuine reasonable excuse and the failure was not deliberate.
There is also a practical reason not to leave it: HMRC needs time to process your registration and issue your reference number before you can file. Registering close to the January filing deadline leaves no margin if anything goes wrong.
How to register and get your UTR
Registering as newly self-employed tells HMRC two things at once: that you need to file a Self Assessment return, and that you are trading as a sole trader for National Insurance. The route for the self-employed is the CWF1 registration, which you can complete online through HMRC. Most dentists register online; a postal CWF1 form is available if you cannot use the online service.
What you need
- Your National Insurance number.
- Basic personal details and contact information.
- The date you started self-employed dental work.
- The nature of your work (dentistry / dental services).
What happens step by step
- You set up or sign in to a Government Gateway account, which is your secure login for HMRC online services.
- You complete the self-employed registration (CWF1) and submit it.
- HMRC issues you a Unique Taxpayer Reference (UTR), a ten-digit number that identifies you for Self Assessment. This arrives by post and can take a couple of weeks, sometimes longer in busy periods.
- You then activate your Self Assessment online account so you can file when the time comes.
Keep your UTR safe. You will need it every year to file, and your accountant will ask for it if you appoint one. If you already have a UTR from a previous spell of self-employment, you do not get a new one, but you should still tell HMRC you have started trading again.
If you also have PAYE income
Plenty of dentists have a foot in both camps: a salaried hospital or community post, or a foundation or training role, alongside self-employed associate or locum sessions. Mixed income is common and entirely manageable, but it does mean you must register.
A few points to hold onto:
- You still register on the self-employed basis for your associate or locum income, even though your salary is already taxed under PAYE.
- PAYE does not cover the self-employed side. Your employer deducts tax only on your salary. The tax on your self-employed profit is settled through Self Assessment.
- Your return brings both together. When you file, you report your PAYE earnings and the tax already deducted, alongside your self-employed profit, so the figures reconcile and you are not taxed twice on the same income.
- Watch your tax code. Earning across two sources can push part of your income into a higher band, so the tax on your self-employed profit can be higher than you expect.
What happens after you register
Once you are registered and have your UTR, you are in the Self Assessment system and a yearly rhythm begins.
- Annual filing. You file a return for each tax year. The online filing and payment deadline is 31 January following the end of the tax year (so 31 January 2027 for 2025/26).
- Income tax on profit. Your profit, after allowable expenses, is taxed at the usual rates after your personal allowance.
- National Insurance. Self-employed dentists pay Class 4 NIC at 6% on profits between 12,570 and 50,270 pounds and 2% above that. Separate weekly Class 2 contributions are no longer charged: from 6 April 2024, self-employed people with profits at or above the small-profits threshold are treated as having paid and keep their state-pension entitlement, so you do not pay a flat weekly Class 2 amount.
- Payments on account. Where your bill exceeds a small threshold, HMRC asks for two advance payments towards the next year, due 31 January and 31 July, each broadly half of the prior year's liability. In your first self-employed year this can make the January bill feel like more than a single year of tax. We explain it in full in our guide to the newly qualified dentist's first Self Assessment.
- Making Tax Digital. Digital record-keeping and quarterly updates are being phased in for income tax. Most full-time associates and unincorporated principals are caught from 6 April 2026 (qualifying income above 50,000 pounds), so it is worth setting up tidy digital records from the start.
From day one, keep good records: every source of income, your allowable expenses, and any tax already deducted through PAYE. Clean records make filing faster and protect your position if HMRC ever asks.
Common registration mistakes
- Assuming you are employed. Working mostly at one practice does not make you employed. Most associates are self-employed and must register.
- Ignoring small or occasional income. A few private or sessional sessions still count.
- Leaving it until the return is due. Registration and filing are separate steps. Waiting until January risks missing the 5 October deadline and leaves no time for your UTR to arrive.
- Forgetting a previous UTR. If you have been self-employed before, reactivate rather than registering from scratch.
Getting it right from the start
Registration is the easy part to get right and the easy part to get wrong by leaving it too late. Diarise the 5 October deadline for the year you start, register online, and keep your UTR somewhere safe. If your situation is more involved, such as mixed PAYE and self-employed income, a move into a limited company, or partnership profit shares, a specialist dental accountant can confirm exactly what you need to register and file, and make sure you are compliant from your first year. For the full picture of how associate income is taxed once you are registered, read our associate dentist tax guide.