Most locum dentists are self-employed across several practices — which means one self assessment return, but income and paperwork arriving from many directions. The principles are the same as for any associate. The failure mode is different: records scattered across sites and engagements until nobody can reconstruct the year, and two specific rules — travel and NHS pension — that behave differently for locums than for anyone else in dentistry.
However many practices you work at, you have one trade and file one self assessment return. That sounds simpler than it is, because the paperwork arrives in a dozen formats: pay statements from some practices, self-billing invoices from others, agency remittances, and the occasional handwritten figure. Keep a single running record with one row per payment — practice, dates worked, gross paid, deductions taken, net received — and file the underlying statement as you go. Reconstructing this in January from bank entries is where locums lose money, because a bank credit tells you the net figure and nothing about what was deducted to get there.
Locums are often told their travel is fully claimable because they work at multiple sites. That is not the test, and the distinction has been litigated.
The favourable position comes from Horton v Young, where a bricklayer working at a succession of genuinely temporary sites, with no fixed base at any of them, could deduct his travel: the work was itinerant by its nature. The restrictive position comes from Samadian v HMRC, a self-employed medical consultant who held regular, predictable sessions at private hospitals. The tribunal treated those hospitals as places of business, so travel from home to them was ordinary commuting and not deductible — even though he had a genuine office at home and worked at several sites.
The pattern of the engagement decides, not the number of practices. A booking taken for three days next month at a practice you have never visited is a temporary engagement. A standing Monday slot you have filled at the same practice every week for two years has become a place of business, whatever the contract calls it. Travel between practices on a multi-site day is deductible in either case.
From 6 April 2026 the flat mileage rate for cars and vans rose from 45p to 55p for the first 10,000 business miles in the tax year, with 25p a mile above that. Motorcycles remain at 24p and bicycles at 20p. The increase applies to the self-employed simplified mileage rates as well as to employee mileage payments, and it is the first change in fifteen years — so a locum still working to 45p is understating a real deduction.
Take an illustrative locum with £96,000 of gross fees across five practices, logging 9,400 business miles. Of those, 2,600 are home-to-practice journeys for a weekly slot held for two years — a place of business under the Samadian reasoning, so not claimable. The remaining 6,800 miles are one-off bookings and practice-to-practice travel:
On profits above £50,270 the marginal cost is 40% income tax plus 2% Class 4 National Insurance, so that £680 of extra deduction is worth roughly £286 of tax, and the £1,430 of over-claim is roughly £601 of tax that would have to be repaid with interest. Log every journey with its purpose and the practice attended; the log is what makes the claim defensible.
A locum dentist can be a member of the NHS Pension Scheme, but only on the right kind of work. The conditions are specific: you must be a qualified dentist, working at a GDS or PDS practice on an occasional basis, and performing on that practice's GDS or PDS contract. Self-employed performers submit their net pensionable earnings annually through Compass.
The trap is agency work. Earnings received through an agency cannot be pensioned, and neither can work the practice has subcontracted out. A locum billing £96,000 of which £30,000 came via an agency has, at most, £66,000 of potentially pensionable earnings — and no amount of paperwork afterwards converts the agency portion. If NHS pension membership matters to you, that makes the routing of a booking a pension decision as much as a commercial one, and it needs asking before you accept, not at year end. Our NHS pension page covers what we reconcile for practitioner clients each year.
Short engagements controlled tightly by the practice can drift towards employment in substance. The indicators are the familiar ones: who decides your hours, whether you can send a substitute, whether you are integrated into the practice's rotas and management in a way a genuine contractor would not be. Status surprises cut both ways — an engagement that is employment in substance changes both the tax and the entitlements — so read each agreement rather than assuming the label on it settles the question.
Making Tax Digital for Income Tax has applied since 6 April 2026 to anyone whose qualifying income exceeded £50,000 on their 2024/25 return, dropping to £30,000 from April 2027 and £20,000 from April 2028. Qualifying income is total turnover from self-employment and property before any expenses, so the £96,000 locum above is comfortably inside it even though their taxable profit is far lower. Quarterly updates are due 7 August, 7 November, 7 February and 7 May. There are no penalties for missing a quarterly update deadline in the 2026/27 tax year, but the record-keeping requirement is real from now. See our note on the MTD position for dentists.
Gaps between bookings are normal, and nothing collects tax for you. Set aside 30% of every payment received, plus a separate buffer for quiet months, and treat the tax account as untouchable. Two other dates bite: payments on account fall due each 31 January and 31 July if your last tax bill exceeded £1,000 and less than 80% of it was collected at source — which describes almost every locum. Class 4 National Insurance runs at 6% on profits between £12,570 and £50,270 and 2% above, and Class 2 sits at £3.65 a week, with contributions credited automatically once profits reach £7,105.
Run properly — one clean record system, quarterly check-ins, expenses logged with the travel pattern documented — a locum's tax is no harder than anyone else's. Run from a shoebox across nine practices, it is misery, and the mileage log is usually the first thing to go. We onboard locums onto exactly that system as standard.
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Sometimes, and the pattern of the engagement decides. In Horton v Young a tradesman moving between genuinely temporary sites with no fixed base could deduct his travel, because the work was itinerant by nature. In Samadian v HMRC a self-employed consultant holding regular, predictable sessions at private hospitals could not, because those hospitals were places of business and the journey was ordinary commuting. A three-day booking at an unfamiliar practice sits on the first side of that line; a standing weekly slot you have held for two years sits on the second. Travel between practices on a multi-site day is deductible either way, so log every journey with its purpose.
From 6 April 2026 the flat rate is 55p a mile for the first 10,000 business miles in the tax year and 25p a mile above that, for cars and vans. Motorcycles are 24p and bicycles 20p. This was the first change since 2011 — the car rate had been 45p for fifteen years — and it applies to the self-employed simplified mileage rates as well as to employee reimbursement. On 6,800 allowable business miles the deduction is £3,740 rather than the £3,060 the old rate would have given. If you use simplified mileage you cannot also claim actual running costs or capital allowances for the same vehicle, so the choice is made per vehicle and kept consistent.
It can be, but the conditions are narrow. You must be a qualified dentist working at a GDS or PDS practice on an occasional basis, performing on that practice's GDS or PDS contract, and you submit your net pensionable earnings annually through Compass. The significant exclusion is agency work: earnings received through an agency are not pensionable, and neither is work the practice has subcontracted out. A locum billing £96,000 with £30,000 routed through an agency has at most £66,000 of pensionable earnings, and that cannot be corrected later. Ask how a booking is contracted before accepting it if scheme membership matters to you.
For most of them, yes. It has applied since 6 April 2026 to anyone whose qualifying income was over £50,000 on their 2024/25 return, and the threshold falls to £30,000 from April 2027 and £20,000 from April 2028. Qualifying income is total turnover from self-employment and property before expenses, not profit, so a locum grossing £96,000 across five practices is inside it regardless of what their taxable profit turns out to be. Quarterly updates are due 7 August, 7 November, 7 February and 7 May. No penalties apply to late quarterly updates for the 2026/27 tax year, but the digital record-keeping obligation applies now.
Thirty per cent of every payment received is the working rule, held in a separate account and treated as untouchable, with a further buffer for quiet months because locum income is uneven. The reason the figure is not lower is that two liabilities stack: income tax at 20% or 40% depending on where your profit falls against the £12,570 personal allowance and the £50,270 higher rate threshold, plus Class 4 National Insurance at 6% between those two figures and 2% above. Payments on account then fall due each 31 January and 31 July where your previous bill exceeded £1,000 and under 80% was collected at source, which covers almost every locum.
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