Filing your dentist self assessment tax return does not need to be overwhelming. Whether you are a self-employed associate, a locum across several practices or an unincorporated principal, understanding what to report, which costs you can deduct and when payment is due keeps you compliant and stops you handing HMRC more than you owe.
This guide covers the whole annual cycle for the current 2026/27 tax year: who has to file, the income to declare, allowable expenses, Class 4 National Insurance, payments on account, the deadline calendar, how to file, and the Making Tax Digital change that lands on 6 April 2026. Registration mechanics (getting your Unique Taxpayer Reference for the first time) are covered in depth on our Self Assessment registration guide for dentists, so this page concentrates on the filing itself.
Who needs to file a dentist Self Assessment?
Most dentists in the UK need to complete a return. You are in scope if you are:
- An associate dentist with self-employment income above the £1,000 trading allowance
- An unincorporated practice owner (sole trader or partner) with business profits
- A locum working self-employed across multiple practices
- A mixed NHS and private associate drawing fee-split or per-UDA income
- A salaried or employed dentist with private, locum or teaching income on the side, or with total income over £150,000
Status matters here. A dental associate is normally self-employed for tax, but that rests on the substance of the working arrangement rather than the label on the contract: HMRC weighs control, personal service, financial risk and integration. The BDA model associate agreement supports self-employed status, it does not guarantee it. A newly qualified dentist in foundation training (DFT) is different again: during the DFT year you are a salaried PAYE employee and an NHS Pension officer, and Self Assessment only begins once you move to self-employed associate work.
The Self Assessment deadline calendar
The dates run on the same schedule as any other self-employed professional. Working through a 2025/26 tax year (6 April 2025 to 5 April 2026) as the example:
| Deadline | What is due |
|---|---|
| 5 October 2026 | Register for Self Assessment if 2025/26 is your first year of self-employment |
| 31 October 2026 | Paper tax return must reach HMRC |
| 31 January 2027 | Online return filed, balancing payment for 2025/26 paid, and first payment on account for 2026/27 paid |
| 31 July 2027 | Second payment on account for 2026/27 paid |
Almost every dentist files online, which gives until 31 January. The paper deadline of 31 October is three months earlier and rarely practical given a clinical diary. Note that the registration deadline only bites in your first year: once you have a UTR you simply file each year.
What late filing and late payment cost
The penalties are automatic and apply even when no tax is owed. File late and you face an immediate £100 penalty, then £10 a day after three months (capped at £900), then 5% of the tax due or £300 (whichever is greater) at six months, and the same again at twelve months. Pay the tax late and a separate 5% surcharge applies at 30 days, six months and twelve months, with interest running on the unpaid amount from the original due date. The cheapest return is the one filed on time.
What income to report
Calculate your total income for the tax year (6 April to 5 April). On the self-employment pages declare everything from your dental work:
- Associate fees from every practice (NHS fee-split, per-UDA and private)
- Private treatment income earned in your own right
- Locum payments
- Teaching, examining, mentoring and consultancy fees
If you also have employed income, the P60 or P45 figures go on the employment pages, and any savings, dividend or rental income has its own section. For a mixed associate, keeping the NHS and private streams clearly separated through the year makes the return faster and underpins the kind of analysis in our note on the NHS and private income mix.
Allowable expenses for dentists
You may deduct costs incurred wholly and exclusively for the trade. The common dental categories are:
- Professional indemnity: Dental Protection, the MDU or MDDUS
- GDC annual retention fee and specialist-register fees (the restoration fee and any CPD-shortfall penalty are not allowable)
- Approved subscriptions: bodies on HMRC's List 3, such as the BDA, the FGDP and specialty societies
- CPD genuinely relevant to your current practice (training that creates a wholly new skill can be capital, not a revenue deduction)
- Loupes, instruments and equipment: usually relieved through capital allowances and the Annual Investment Allowance rather than as a simple expense
- Travel between practices: business mileage, but not home-to-regular-practice commuting
- Home-office, phone and internet on a fair business apportionment
- Accountancy fees, business bank charges and business-loan interest (the interest only, never the loan principal)
Two points trip dentists up most often. First, the mileage rate. From 6 April 2026 HMRC's approved rate for cars and vans is 55p per mile for the first 10,000 business miles (up from 45p, which still applies to 2025/26 and earlier years) and 25p per mile thereafter. So a year that straddles the change uses 45p up to 5 April 2026 and 55p from 6 April 2026. Second, the home-to-first-practice journey is ordinary commuting and is never deductible; travel between practices during the working day is. For a deeper walk through every category, including the records HMRC expects, see our associate dentist allowable expenses guide.
Class 4 National Insurance and the Class 2 change
Self-employed dentists pay Class 4 National Insurance through Self Assessment, calculated automatically on your profits:
- 6% on profits between £12,570 and £50,270
- 2% on profits above £50,270
The main Class 4 rate was cut from 9% to 6% with effect from 2024/25, so any older guidance quoting 9% is out of date. Class 2 National Insurance was abolished from 6 April 2024. Self-employed dentists with profits at or above the small-profits threshold are now treated as having paid Class 2, keeping their state pension and benefit record intact with no separate weekly charge. Only a dentist with profits below the threshold who wants to protect their record needs to consider paying Class 2 voluntarily. Do not pay a weekly Class 2 charge you no longer owe.
Combined with income tax (basic 20%, higher 40%, additional 45%, with the personal allowance of £12,570 tapering away once income passes £100,000), the self-employed marginal rates work out at roughly 26% in the basic band, 42% in the higher band and 47% at the additional rate.
Payments on account explained
If your Self Assessment liability exceeds £1,000 and less than 80% of your tax was collected at source, HMRC asks you to pay next year's tax in advance through payments on account. Each instalment is 50% of the prior year's liability:
- First payment on account: due 31 January (alongside the balancing payment for the year just filed)
- Second payment on account: due 31 July
The shock lands in your first self-employed January. Take an associate whose first full-year liability is £10,000. That January they pay the £10,000 balancing payment for the year just gone plus a £5,000 first payment on account for the current year, a £15,000 bill in one month, then a further £5,000 the following July. After that the system smooths out, but the first year needs planning for. If your income has genuinely fallen you can apply to reduce your payments on account, though under-reducing leaves interest to pay. Our guide for the newly qualified dentist's first payments on account works the timing through in full.
How to file your return, step by step
Once you have your UTR and a Government Gateway account, filing follows a clear sequence.
Step 1: Gather your figures
Pull together income records from every practice, expense receipts and mileage logs, business bank statements, and any P60 or P45 for employed income. Tot up the totals before you log in.
Step 2: Tailor the return
HMRC's online service asks which pages you need. Add the self-employment section, plus employment, dividend, savings or property sections if they apply to you.
Step 3: Enter income and expenses
Put your turnover and allowable expenses on the self-employment pages. The system then calculates your trading profit, the income tax and Class 4 NIC due, and any payments on account.
Step 4: Review the calculation
Check the figures before you submit. Confirm the tax year is correct, that no income source is missing and that the payments on account look right against last year.
Step 5: Submit and pay
File the return and set up payment well before 31 January. A Budget Payment Plan or a standing order through the year takes the sting out of the January bill.
Common mistakes to avoid
- Mixing personal and business costs: only the business proportion is allowable, so apportion phone, car and home costs honestly
- Claiming home-to-practice travel: ordinary commuting is never deductible
- Using stale figures: a 9% Class 4 rate, a weekly Class 2 charge or a 45p mileage rate after 5 April 2026 are all out of date
- Forgetting payments on account: budget for the January double bill in your first self-employed year
- Thin records: HMRC can disallow poorly evidenced claims, so keep receipts and a contemporaneous mileage log
For the wider picture of how an associate's tax position fits together, our associate dentist tax guide sets out the full framework.
Making Tax Digital from 6 April 2026
The biggest change to how dentists file is now here. Making Tax Digital for Income Tax (MTD for ITSA) mandates digital record-keeping and quarterly updates to HMRC, phased in by qualifying income (your gross trading plus property income, tested on the relevant prior year's return):
- Over £50,000: from 6 April 2026
- Over £30,000: from 6 April 2027
- Over £20,000: from 6 April 2028
Most full-time associates and unincorporated principals turn over well above £50,000, so they are in scope from 6 April 2026. In practice that means keeping records in MTD-compatible software, sending a summary to HMRC each quarter and then a final declaration after the tax year, in place of the single annual return. Limited companies are not affected (MTD for ITSA is income tax, not corporation tax). If you still keep your books in a spreadsheet or a shoebox, now is the time to move to compatible software. Our Making Tax Digital guide for dental practices sets out the practical readiness steps.
Planning ahead
The dentists who find Self Assessment painless are the ones who prepare through the year rather than scrambling in January. A few habits make the difference:
- Set aside a monthly tax provision (a useful rule of thumb is 25% to 30% of net profit, more once you are into the higher rate)
- Keep digital records as you go, which doubles as MTD preparation
- Time larger equipment purchases to make the most of the Annual Investment Allowance
- Consider pension contributions, which can be a tax-efficient way to reduce your liability
Filing well is the floor, not the ceiling. As income grows, or when you start thinking about incorporation, a partnership or buying a practice, the planning questions get more valuable than the compliance ones. A specialist dental accountant who understands NHS and private income, the pension interaction and the sector's quirks will usually find more than they cost. If you would like a second pair of eyes on your position, speak to a specialist dental accountant before your next return is due.