Self Assessment Tax for GP Locums: Expenses, NI, and Deadlines

As a self-employed GP locum, you handle your own tax through HMRC’s Self Assessment system: you register as a sole trader, track your income and allowable expenses across the tax year, then file a return online and pay what you owe by 31 January. Class 4 National Insurance is calculated on the same return. The rules on GP locum Self Assessment tax are the same as for any other sole trader, but a few things (NHS pension paperwork, mileage between practices, indemnity fees) matter more for locums than most.

When to Register With HMRC

If your gross self-employed income for a tax year is more than the £1,000 trading allowance, you have to notify HMRC and register for Self Assessment.1HM Revenue & Customs. Tax-Free Allowances on Property and Trading Income A locum passes that threshold within a few sessions, so treat registration as compulsory from the point you start taking work.

The deadline is 5 October following the end of the tax year in which you first earned self-employed income.2GOV.UK. Self Assessment Tax Returns – Deadlines If your first locum session fell between 6 April 2025 and 5 April 2026, you have until 5 October 2026 to register. You do it online as a sole trader through the HMRC website. HMRC will issue you a ten-digit Unique Taxpayer Reference, normally within ten working days.3GOV.UK. Find Your UTR Number That UTR gets you into the Government Gateway portal where you file.

Holding a salaried post at a practice alongside your locum work does not exempt you. PAYE takes care of the salaried income; the locum earnings still have to be reported separately, and the Self Assessment return pulls both together to work out your total liability.

Tracking Income and Expenses Across the Year

The UK tax year runs from 6 April to 5 April. Every session, invoice, and expense in that window needs to be captured. Cash basis accounting is now the default for sole traders: you record income when it lands in your account and expenses when you actually pay them.4GOV.UK. Cash Basis – Overview An invoice you raised in March but that gets paid in May falls into the following tax year.

Keep every invoice you issue to practices, integrated care boards, and out-of-hours services. If you also had salaried work, gather your P60 or P45 too, because previously taxed employment income affects the calculation.5GOV.UK. Your P45, P60 and P11D Form

Self-employed figures go on the SA103 supplementary page, filed with the main SA100 return. Below the VAT threshold you use the short form (SA103S); above it, the full version (SA103F).6GOV.UK. Self Assessment – Self-Employment (Short) (SA103S) Both split turnover from business expenses so HMRC can see your taxable profit.

Expenses a GP Locum Can Deduct

Every legitimate business expense reduces your taxable profit. To qualify, the cost must be incurred “wholly and exclusively” for your work; anything with a personal element is disallowed or has to be apportioned.

  • Professional registration and subscriptions: your GMC fee, BMA membership, Royal College subscriptions, and similar professional body fees are all deductible.
  • Medical indemnity insurance: payments to bodies like the Medical Defence Union or Medical Protection Society count as a business expense.
  • Travel between practices: mileage at 45p per mile for the first 10,000 business miles in the tax year, then 25p per mile after that. If you work at one practice so regularly that it becomes your permanent workplace, travel there counts as commuting and is not deductible.7GOV.UK. Travel – Mileage and Fuel Rates and Allowances
  • Working from home: a flat monthly rate based on hours worked — £10 for 25 to 50 hours, £18 for 51 to 100 hours, £26 for 101 hours or more. The flat rate covers utilities but not phone or internet; those you claim separately based on the business share of actual costs.8GOV.UK. Simplified Expenses if You’re Self-Employed – Working From Home
  • Training and CPD: courses that maintain or update existing skills are deductible, along with related travel and study materials. Training leading to an entirely new qualification is treated as capital expenditure and cannot be deducted.

Keep receipts and records for everything. Accounting software makes this painless, and it will matter more once Making Tax Digital takes effect.

Income Tax and the Personal Allowance

Subtract allowable expenses from gross income and what remains is your taxable profit. Everyone gets a tax-free personal allowance of £12,570 before income tax applies. Above that, the rates for taxpayers in England, Wales, and Northern Ireland are 20% on taxable income from £12,571 to £50,270, 40% from £50,271 to £125,140, and 45% above £125,140.9GOV.UK. Income Tax Rates and Personal Allowances

Watch the £100,000 threshold. The personal allowance tapers away above it: you lose £1 for every £2 earned over £100,000, and the allowance disappears entirely at £125,140. The effective marginal rate between those two figures is 60%, which makes pension contributions and other reliefs particularly valuable in that band.

Scotland sets its own income tax bands. If you’re a Scottish taxpayer, check the Scottish rates on GOV.UK when working out your liability.

National Insurance for Self-Employed Locums

Two classes apply, but only one usually requires payment. Class 2 protects entitlement to the State Pension and certain benefits. If your profits are £6,845 or more, Class 2 is treated as paid automatically and you owe nothing.10GOV.UK. Self-Employed National Insurance Rates Below £6,845 you can pay voluntarily at £3.50 per week to keep your record intact.

Class 4 is the one that costs money. For 2025-26, that’s 6% on profits between £12,570 and £50,270, plus 2% on anything above £50,270.10GOV.UK. Self-Employed National Insurance Rates It’s calculated as part of your Self Assessment return, so you don’t file anything separate.

If there are gaps in your National Insurance record from earlier years, voluntary Class 3 contributions can fill them and may increase your State Pension. You have up to six years to fill a gap; check your record through your personal tax account before paying.11GOV.UK. Pay Voluntary Class 3 National Insurance

NHS Pension Contributions and the Locum Forms

Most GP locums contribute to the NHS Pension Scheme, and those contributions attract tax relief. The mechanism runs through Locum A and Locum B forms. Each practice you work at completes a Locum A recording your pensionable pay for the session. You then submit a Locum B to Primary Care Support England, aggregating your contributions across every practice.12Primary Care Support England. Submit Locum A and B Forms

At Self Assessment, your pension contributions reduce the income on which you pay tax. For higher-rate locums, the relief is substantial. Collect Locum A forms from every practice promptly. Chasing them down months later is one of the most common headaches at filing time, and missing forms usually mean understated contributions and overpaid tax.

Filing Deadlines and How to Pay

File online through the Government Gateway using the credentials set up at registration. The system walks you through the SA100 and any supplementary pages, gives you a summary to review, and issues a confirmation receipt on submission. Save it.

Payments on account are advance payments against next year’s bill. Each is half of the previous year’s liability. If your income drops, you can apply to reduce them, but underestimate and HMRC will charge interest on the shortfall.

Same-day or next-day payment options include online banking, Faster Payments, CHAPS, and debit or corporate credit card. Direct Debit, Bacs, and cheque take three to five working days to clear.14GOV.UK. Pay Your Self Assessment Tax Bill Personal credit cards are not accepted.

Two adjacent liabilities can also surface through your return. If you’re repaying a student loan, the return works out repayments at 9% of income above the relevant plan threshold, aggregating employment and self-employment income and offsetting anything already taken through PAYE. And if you or your partner claim Child Benefit and either of you earns more than £60,000, the High Income Child Benefit Charge claws back 1% of the benefit per £200 of income above £60,000, rising to a full clawback at £80,000.15GOV.UK. High Income Child Benefit Charge

Penalties for Late Filing, Late Payment, and Errors

Miss the 31 January filing deadline and you incur an immediate £100 penalty, even if you owe no tax. After three months, daily penalties of £10 start, capped at £900. At six months, a further 5% of the tax due or £300 applies, whichever is greater. At twelve months, the same charge again.16GOV.UK. Self Assessment Tax Returns – Penalties

Late payment attracts interest at 7.75% per year on the outstanding balance.17GOV.UK. HMRC Interest Rates for Late and Early Payments The rate jumped when HMRC changed its formula in April 2025 to base rate plus 4%, so carrying a balance is significantly more expensive than it used to be.

Inaccuracies on the return have a separate penalty regime. A careless mistake can cost 0% to 30% of the extra tax due. A deliberate inaccuracy attracts 20% to 70%, and deliberate inaccuracies you’ve tried to conceal sit in a 30% to 70% range. Disclosing mistakes voluntarily before HMRC finds them substantially reduces the penalty in every category.

Fixing Mistakes and Payment Difficulties

Spot an error after filing and you can amend the return up to twelve months after the 31 January following the end of the tax year. For a 2025-26 return filed by 31 January 2027, you have until 31 January 2028 to amend. You do it through your online account and can submit as many amendments as needed before the deadline.2GOV.UK. Self Assessment Tax Returns – Deadlines Miss the amendment window and you’ll need to write to HMRC.

If you cannot pay in full by 31 January, don’t ignore it. HMRC offers Time to Pay arrangements that spread the cost across monthly instalments. If your debt is £30,000 or under and your return is filed, you can set up a plan online through your HMRC account.18GOV.UK. If You Cannot Pay Your Tax Bill on Time – Setting Up a Payment Plan Larger amounts need a call to HMRC’s payment support line. Interest still runs while you’re on a plan, but it is far better than ignoring the bill and triggering enforcement.

Making Tax Digital From April 2026

This is the biggest change to self-employed tax reporting in years, and it affects most GP locums. Making Tax Digital for Income Tax becomes mandatory from 6 April 2026 if your qualifying income from self-employment and property exceeded £50,000 on your 2024-25 return.19GOV.UK. Find Out if and When You Need to Use Making Tax Digital for Income Tax From April 2027, the threshold drops to £30,000. Given typical locum earnings, most full-time locums fall into the first wave.

Under MTD you’ll need compatible accounting software to keep digital records, send quarterly summary updates to HMRC, and file the annual return through the software rather than the Government Gateway portal.20GOV.UK. Choose the Right Software for Making Tax Digital for Income Tax The quarterly updates aren’t tax returns; they’re summaries of income and expenses for the quarter. HMRC has published a tool to help you find compatible software.

The first quarterly deadline for the 2026-27 tax year is 7 August 2026, covering 6 April to 5 July. HMRC has said it won’t apply penalty points for late quarterly updates in the first year of operation.21GOV.UK. Sign Up for Making Tax Digital for Income Tax Payment deadlines don’t change: 31 January and 31 July stay as they are.

If you aren’t already on accounting software, get on it now. The shift from annual paper-chasing to quarterly digital reporting requires a different workflow, and figuring it out in April 2026 when it becomes compulsory will be more stressful than putting a system in place first.

How Long to Keep Your Records

Keep all business records for at least five years after the 31 January submission deadline for the relevant tax year.22GOV.UK. Business Records if You’re Self-Employed – How Long to Keep Your Records For a 2025-26 return due 31 January 2027, that means retaining records until 31 January 2032. If you file more than four years late, the retention period runs 15 months from the date you actually submit. Invoices, bank statements, expense receipts, Locum A and B forms, mileage logs, and P60s all count. Digital records stored securely in cloud accounting software satisfy the obligation as well as paper files.