What This Guide Covers

Filing a tax return as a locum dentist in the UK is not the same as filing as an associate or a practice owner. Your income pattern, allowable expenses, IR35 exposure, and pension contributions all differ. This guide walks you through the process step by step for the 2025/26 tax year, using real figures and practical examples.

If you are a locum working through a limited company, the rules are different again. This article focuses on locum dentists who are self-employed sole traders. If you operate through a personal service company (PSC), see our guide on locum dentist tax for limited company contractors.

Step 1: Register for Self-Assessment

If you have not filed a self-assessment tax return before, you must register with HMRC. Do this as soon as you start locum work, not after the tax year ends. The registration process gives you a Unique Taxpayer Reference (UTR) and activates your online account.

To register as self-employed, go to gov.uk and complete the online form. HMRC will send you a UTR by post within 10 working days. You can then activate your Government Gateway account and access your HMRC online services.

Deadline note: You must register by 5 October following the end of the tax year in which you started self-employment. For example, if you started locum work in September 2025, you must register by 5 October 2026. Missing this deadline triggers a £100 penalty.

What if HMRC already sends me a return?

If you previously filed a return as an employed dentist or associate, you may already have a UTR. Check your HMRC online account. You will need to add a self-employment source to your existing return. Do this through your online account or by calling the Self Assessment helpline.

Step 2: Record All Locum Income Accurately

Your locum income includes all fees received from practices for covering sessions, whether NHS or private. You must record the gross amount before any deductions for lab fees, materials, or surgery rent. Do not net off expenses at the income recording stage.

Example: You locum at three practices in a month. Practice A pays you £2,400 for 8 sessions. Practice B pays £1,800 for 6 sessions. Practice C pays £3,100 for 10 sessions. Your total gross income for that month is £7,300. Record this as your turnover, not the net amount after expenses.

Keep a running total of your income month by month. Use accounting software such as FreeAgent, Xero, or QuickBooks, or maintain a spreadsheet. HMRC expects you to keep records for at least 5 years after the 31 January filing deadline.

NHS vs private income

Distinguish between NHS and private income on your records. This matters for two reasons. First, your NHS pension contributions are calculated on NHS income only. Second, if you claim mileage or other expenses, the split affects the proportion you can deduct if you use the same car for both types of work.

For NHS locum work, you will receive a payment from the NHS Business Services Authority (NHSBSA) or the relevant health board. Keep all payment schedules and remittance advices. For private locum work, the practice pays you directly. Issue an invoice for each engagement and keep a copy.

Step 3: Claim Allowable Expenses Correctly

As a self-employed locum dentist, you can claim a wide range of expenses against your locum income. The key principle is that the expense must be incurred wholly and exclusively for the purposes of your trade. HMRC tests this strictly.

Common allowable expenses for locum dentists

  • Travel and mileage: You can claim mileage at HMRC-approved rates (45p per mile for the first 10,000 business miles, 25p thereafter). This covers travel between your home and each practice where you locum. You cannot claim for ordinary commuting from home to a permanent workplace, but as a locum with no fixed practice, each engagement is a temporary workplace. Keep a mileage log.
  • Professional fees and subscriptions: GDC annual retention fee, indemnity insurance (MDU, Dental Protection, MDDUS), BDA membership if relevant, and any other professional body subscriptions.
  • CPD and training: Course fees, travel, accommodation, and materials for verifiable CPD. The GDC requires 100 hours over 5 years. All costs are allowable if the training maintains or improves your professional skills.
  • Equipment and instruments: Handpieces, burs, loupes, headlights, and other clinical equipment. Items costing less than £2,000 can be expensed in full under the Annual Investment Allowance (AIA). More expensive items are capitalised and claimed over several years.
  • Insurance: Public liability insurance, income protection insurance, and professional indemnity.
  • Accountancy fees: Fees paid to a dental-specialist accountant for preparing your tax return and advising on tax planning.
  • Use of home as office: If you do administrative work at home (booking sessions, invoicing, record keeping), you can claim a proportion of your household costs. HMRC accepts a simplified rate of £6 per week without needing to calculate actual costs, or you can claim a proportion of rent, mortgage interest, utilities, and broadband based on the number of rooms used and hours worked.

Expenses you cannot claim

You cannot claim for ordinary clothing, even if you wear it only for work. Dental scrubs and tunics are an exception if they are specific to your role and not suitable for everyday wear. You also cannot claim for fines, penalties, or the cost of entertaining clients (though entertaining staff is allowable).

Step 4: Understand IR35 and Your Working Arrangements

IR35 is the off-payroll working rules that apply when a locum dentist works through a limited company. If you are a sole trader, IR35 does not apply directly. However, the principles of employment status still matter for your tax return.

HMRC may challenge your self-employed status if your working arrangements look like employment. The key tests are:

  • Control: Does the practice control when, where, and how you work? If they dictate your hours, treatment plans, and clinical decisions, you look more like an employee.
  • Substitution: Can you send another locum in your place if you are unavailable? If not, that weakens your self-employed status.
  • Mutuality of obligation: Is the practice obliged to offer you work, and are you obliged to accept it? If yes, that points to employment.
  • Financial risk: Do you bear financial risk (e.g., you pay for your own indemnity, equipment, and training)? If yes, that supports self-employment.
  • Integration: Are you integrated into the practice team, attending staff meetings and using practice email? If yes, that can indicate employment.

Most locum dentists working on a session-by-session basis with their own indemnity and equipment are genuinely self-employed. But if a practice treats you like an employee in practice, HMRC may reclassify you. Keep a record of your contracts and working arrangements to defend your status if challenged.

For more detail, see our associate tax survival guide, which covers similar principles for associates.

Step 5: Handle Your NHS Pension Contributions

As a locum dentist providing NHS treatment, you can contribute to the NHS Pension Scheme. The rules depend on whether you are a tier 1 or tier 2 locum.

Tier 1 locum: You work for an NHS body (e.g., a community dental service or hospital) and are treated as an employee for pension purposes. Your employer deducts contributions from your pay.

Tier 2 locum: You work for a non-NHS body (e.g., a private practice providing NHS treatment). You must make your own arrangements to pay pension contributions. You do this by completing a locum application form (available from NHSBSA) and making monthly payments directly.

Your NHS pension contributions are based on your NHS pensionable earnings. You cannot pay into the NHS Pension Scheme on private income. The contributions are tax-deductible as a trade expense on your self-assessment return.

Example: In 2025/26, you earn £45,000 from NHS locum work and £15,000 from private locum work. Your NHS pension contributions (at 9.8% for the 2015 scheme) are £4,410. You can deduct this £4,410 as an expense on your tax return. The £15,000 private income has no NHS pension deduction.

For more on the NHS Pension Scheme, read our NHS pension scheme essentials for dentists.

Step 6: Calculate Your Tax and National Insurance

Once you have totalled your income and deducted your allowable expenses, you arrive at your taxable profit. This is the figure HMRC uses to calculate your income tax and Class 4 National Insurance.

Example calculation for a locum dentist (2025/26):

  • Gross locum income: £72,000
  • Allowable expenses: £8,500 (mileage, indemnity, GDC, CPD, equipment, accountancy)
  • Taxable profit: £63,500
  • Personal allowance: £12,570
  • Taxable at 20%: £37,700 (from £12,571 to £50,270) = £7,540
  • Taxable at 40%: £13,230 (from £50,271 to £63,500) = £5,292
  • Total income tax: £12,832
  • Class 4 NI: 6% on £37,700 (£12,570 to £50,270) = £2,262, plus 2% on £13,230 = £265. Total NI: £2,527
  • Total tax and NI due: £15,359

You pay this through two payments on account (unless your tax bill is under £1,000). The first payment is due by 31 January following the tax year end, the second by 31 July. For 2025/26, the first payment on account is due 31 January 2027, the second 31 July 2027.

Step 7: File Your Return and Pay on Time

The online filing deadline for the 2025/26 tax year is 31 January 2027. The paper filing deadline is 31 October 2026. Most locum dentists file online.

To file online, log into your HMRC account, navigate to Self Assessment, and complete the return. You will need to fill in the self-employment pages (SA103S or SA103F depending on your turnover). You will also need to declare any other income, such as bank interest or dividends.

Late filing penalties:

  • £100 automatic penalty if your return is up to 3 months late
  • Daily penalties of £10 per day (up to 90 days) after 3 months
  • 5% of the tax due (minimum £300) after 6 months
  • Another 5% after 12 months

Late payment interest is charged at the Bank of England base rate plus 2.5%. As of April 2025, this is approximately 7.75% per year.

Step 8: Keep Records for Future Years

HMRC can enquire into your tax return up to 12 months after the filing deadline. Keep all records for at least 5 years after the 31 January deadline. This includes invoices, receipts, mileage logs, bank statements, and pension contribution certificates.

If you use accounting software, export your data annually and store it securely. If you use a spreadsheet, back it up. If you use a dental-specialist accountant, they will typically keep copies of your records and returns.

Common Mistakes Locum Dentists Make on Their Tax Return

  • Not registering for self-assessment early enough. This is the most common error. Register as soon as you start locum work, not after the tax year ends.
  • Claiming mileage without a log. HMRC requires a record of each journey, including date, destination, purpose, and mileage. A spreadsheet or app is sufficient.
  • Mixing up gross and net income. Always record gross income before expenses. Do not net off lab fees or materials at the income stage.
  • Ignoring IR35 when working through a limited company. If you operate through a PSC, the engaging practice (if medium/large) must determine your IR35 status. Get a determination in writing.
  • Forgetting to declare NHS pension contributions. These are deductible expenses. If you pay them directly, include them in your expenses. If your practice deducts them, ensure they are not double-counted.
  • Missing the payments on account. Your first year's tax bill often surprises locums because payments on account mean you pay half of next year's estimated tax early. Plan for this.

When to Use a Dental-Specialist Accountant

Filing your own tax return is possible if your affairs are straightforward. But locum dentists often have multiple income sources, NHS pension complexities, and IR35 considerations that make professional advice worthwhile.

A dental-specialist accountant can:

  • Ensure you claim all allowable expenses correctly
  • Advise on IR35 status and working arrangements
  • Help with NHS pension contribution calculations and elections
  • Plan for payments on account to avoid cash flow surprises
  • Represent you if HMRC opens an enquiry

Accountancy fees are themselves tax-deductible. The cost of professional advice often pays for itself in tax savings and avoided penalties.

Summary: Key Deadlines for Locum Dentists (2025/26)

  • 5 October 2026: Deadline to register for self-assessment if you started locum work in 2025/26
  • 31 October 2026: Paper filing deadline for 2025/26 return
  • 31 January 2027: Online filing deadline and first payment on account for 2025/26
  • 31 July 2027: Second payment on account for 2025/26
  • 31 January 2028: Balancing payment for 2025/26 (if any) and first payment on account for 2026/27

If you are unsure about any aspect of your locum tax return, speak to a dental-specialist accountant who works with locum dentists. The cost of getting it wrong (penalties, interest, and HMRC enquiries) far exceeds the cost of professional advice.