How to Tell HMRC You Have Started Locum Work

Your registration deadline is the 5 October that follows the tax year holding your first paid locum session. Work in June 2026 falls in 2026/27, a year that closes on 5 April 2027, so you have until 5 October 2027. You register through the self assessment service on gov.uk, HMRC issues a Unique Taxpayer Reference, and from then on it expects a return each year: for 2025/26 that means an online return and the tax by 31 January 2027, payments on account from 31 January and 31 July once the bill passes £1,000, and Class 4 National Insurance on the profit. Pensioning the work is separate and much more urgent, because Form A and Form B have to reach PCSE within 10 weeks of the session ending.

When exactly is the deadline?

5 October after the end of the tax year, not 5 October after the session. gov.uk states that you must tell HMRC by 5 October if you need to complete a tax return for the previous year. The tax year runs from 6 April to 5 April, so every session between those dates shares one deadline the following October. That gives a first session in April as much as eighteen months of slack and a session in March barely seven, which is the part people misjudge.

There is a floor underneath it. You must register as a sole trader once you earn more than £1,000 from the work in a tax year, and the £1,000 is income, not profit after expenses. Two or three well paid sessions clear it.

How do you register?

Through the self assessment service on gov.uk, using a Government Gateway account. If you already file a return for another reason, you are adding self employment to an existing record rather than starting a new one. HMRC sets up the self assessment record and issues a Unique Taxpayer Reference, the ten digit number that identifies you from then on. It arrives by post, so build in the wait rather than leaving registration until the deadline week.

Your NHS employment is untouched by any of this. If you hold a salaried post alongside the locum sessions, PAYE and Class 1 National Insurance carry on exactly as before and the return simply reports both sources.

What does HMRC expect after that?

A return every year, filed online by 31 January following the end of the tax year, with the tax due the same day. The paper deadline is three months earlier, 31 October. For the 2025/26 year that is 31 October 2026 on paper and 31 January 2027 online.

Then payments on account. Where your bill exceeds £1,000 and less than 80% of your tax was collected at source, HMRC asks for two interim payments, on 31 January and 31 July, each half of the previous year's liability. This is the shock in the first full year, because the January payment covers the year just filed and half of the next one in a single sum. Budget for it from the first session, not from the first demand.

On the profit you pay income tax at your normal rates plus Class 4 National Insurance, 6% between £12,570 and £50,270 and 2% above that for 2026/27. Class 2 is no longer a required payment: profits at or above the small profits threshold are treated as having paid it, so your state pension record is protected without a weekly charge. Locums below the threshold who want to protect the record can pay voluntary Class 2 at £3.65 a week.

What about the NHS pension?

Registering with HMRC does nothing for your pension. Freelance GP locum work is pensioned on the locum forms, and the deadline is not annual. The practice approves Form A, Form B then goes to PCSE, and PCSE is explicit that work which ended more than 10 weeks ago cannot be pensioned and the form will be rejected. Contributions are paid over no later than the seventh day of the following month. Miss the window and that accrual is gone; it is not a late filing penalty you can settle later. Our guide to Form A and Form B for locums sets out the sequence.

If you also hold a salaried GP post or do solo work, a second piece of paperwork applies: the Type 2 self assessment form, which records the right tiered contribution on that income and runs to a 28 February deadline a year in arrears, so the 2025/26 year is due by 28 February 2027. Contribution tiers sit on pensionable pay and were uplifted from 1 April 2026.

Does Making Tax Digital apply to me?

It applies by gross qualifying income, meaning trading and property income before expenses, tested on the prior year's return. The threshold is £50,000 from 6 April 2026, £30,000 from 6 April 2027 and £20,000 from 6 April 2028. That first tranche is live now, so most full time locums are already inside it and keeping digital records with quarterly updates. Employment income alone does not count towards the figure, and limited companies are outside the regime.

What should you keep from day one?

Records of income and expenses, kept for at least five years after the 31 January submission deadline of the year they relate to. Start on the first session rather than reconstructing it in January.

1. A separate bank account for locum income, so the return is a download rather than an excavation.
2. Every remittance note or invoice, dated and matched to the session.
3. Mileage between sites, with dates and distances. In 2026/27 the approved rate runs at 55p for the first 10,000 business miles and 25p beyond, and the leg from home to wherever you start the day does not count as business travel.
4. Indemnity, GMC retention, Royal College and BMA subscriptions, and any course fees.
5. Copies of every Form A and Form B, with the date the session ended written on them.
6. Equipment purchases, which usually go through capital allowances rather than straight into expenses.

The expenses a locum can claim and the mechanics of the first self assessment return are covered separately. If the question behind the registration is whether the sessions are worth taking alongside a salaried post, and whether a company helps, that decision is worked through in taking locum work as a salaried GP. An accountant who works with locums will take the registration date, the pension forms and the first payment on account together, because they are the three that cost money when they slip.