How a locum's tax works
When a pharmacy pays you as a locum, nobody takes tax off first. The whole invoice lands in your account, and the tax on it is yours to work out, put aside and pay through Self Assessment, months later. That's the single biggest adjustment for anyone who has only ever had a payslip, and the calculator above exists because the sum is harder than it looks.
Three things are taken from your profit, not your turnover. Profit is what's left of your shift earnings after allowable expenses, including your mileage at HMRC's rates.
- Income Tax on your profit plus any other income, after the £12,570 Personal Allowance: 20% up to £50,270, 40% up to £125,140 and 45% above. Scotland has six bands of its own, starting at 19% and reaching 48%.
- Class 4 National Insurance at 6% of profit between £12,570 and £50,270, and 2% above that. Class 2 is no longer owed.
- Student loan repayments, if you have one: 9% of everything over your plan's threshold, collected with your tax rather than from a payslip.
Because the first £12,570 is free and the rates step up, the share of each shift that goes in tax grows through the year. A technician doing two days a week might owe 10% of what they're paid; a pharmacist on five days, 20% or more. The only way to know your share is to work the whole year out, which is what the calculator does.
The set-aside habit
Take the percentage above, round it up a point or two, and move that share of every payment into a separate account the day it arrives. It's dull, and it works. Leave the money in your current account and January becomes a loan from your future self at HMRC's interest rate.
The figure moves as your year changes. Pick up more shifts, cut back, or take a salaried job alongside, and the share changes with it, so check it every few months rather than once in April. Locumoid keeps a running estimate from your actual shifts, so the figure is always for the year you're really having.
The first January
Your first Self Assessment is due on 31 January after the end of your first tax year as a locum. If the bill is £1,000 or more, HMRC also asks for half of it again on the same day as a first payment on account towards the year you're already in, and the other half on 31 July. So your first January bill is a year and a half's tax at once, and it's the reason the calculator shows that date on its own.
The following January settles up: what you really owe for the year, less the two payments you've made, plus the next two halves. From then on it's a rhythm, as long as the money has been set aside all along.
Locum pharmacy technicians
The rules are identical for pharmacy technicians; only the numbers differ. Rates of £15 to £22 an hour mean many technician locums sit entirely within the basic rate band, so the share to set aside is lower, often 10% to 15%. Your GPhC fee, indemnity and travel are deductible in exactly the same way. Choose "Pharmacy technician" above and the calculator starts from typical technician figures.
Questions you might have
How much tax does a locum pharmacist pay?
The same Income Tax as anyone else, on your profit rather than your turnover: nothing on the first £12,570, 20% up to £50,270, 40% up to £125,140 and 45% above that, with Scotland's own bands if you live there. On top of that, Class 4 National Insurance is 6% of profits between £12,570 and £50,270, and 2% above. For a locum pharmacist earning around £55,000 with typical expenses, that comes to roughly a fifth of what they're paid; for a technician on £30,000, closer to an eighth.
What percentage should I set aside from each shift?
There's no single right figure, which is why the rule of thumb of 25% or 30% catches people out both ways: a part-time technician may owe well under 10%, a busy pharmacist nearer 25%. The right share depends on your total for the whole year, because the first £12,570 is tax-free and the rates step up as you earn more. Use the calculator for your own figure, then round it up a little for safety.
Do I pay National Insurance as a self-employed locum?
Yes, Class 4 National Insurance, which is worked out with your Income Tax on your Self Assessment: 6% of profits between £12,570 and £50,270, then 2%. You no longer have to pay Class 2. If your profit is over £7,105 you're credited for your State Pension record without paying it, and below that you can pay it voluntarily, at £3.65 a week, to protect your record.
What are payments on account and why is my first January bill so big?
Once your Self Assessment bill is £1,000 or more, HMRC asks you to pay towards the next year in advance: half your bill on 31 January and half on 31 July. The first January catches new locums out because it's last year's bill plus half of it again, in one go. If your tax bill for 2026/27 is £8,000, you pay £12,000 in January 2028 and £4,000 that July. You're not paying more tax overall, just earlier.
I was employed for part of the year. Does that change things?
Yes. Your employed pay has already used up some of your Personal Allowance and basic rate band, so your locum profit is taxed from where that left off. Put your employed pay for the tax year in the calculator and it works out just the extra tax your Self Assessment will ask for. If 80% or more of your total tax was taken through PAYE, you won't owe payments on account either.
When do I need to register as self-employed?
Tell HMRC by 5 October after the end of the tax year in which you started locuming, so for shifts worked in 2026/27, by 5 October 2027. Your first Self Assessment return and payment are due by 31 January 2028. You register as a sole trader on GOV.UK; it's free, and you get a Unique Taxpayer Reference in the post.
Does my student loan come out of my locum income?
It does, through Self Assessment rather than a payslip. HMRC adds 9% of your income over your plan's threshold (£29,385 for Plan 2, £26,900 for Plan 1, £25,000 for Plan 5) to your January bill, and 6% over £21,000 for a Postgraduate Loan. It isn't included in payments on account, so it's a lump sum each January.
What expenses can a locum pharmacist claim?
Costs that are wholly for your work: your GPhC or PSNI fee, professional indemnity, DBS or PVG check, PDA or other union membership, work travel at HMRC's 55p a mile, parking, training and CPD, a share of your phone, and an accountant's fee. Not your normal clothes, lunches on a normal shift or travel that looks like a regular commute.
Does Making Tax Digital affect me?
If your gross self-employed income is over £50,000 it already does, from April 2026. From April 2027 it applies over £30,000, and from April 2028 over £20,000, so most locums working more than a couple of days a week are in. You'll keep digital records and send HMRC a summary every quarter, with a final return after the year end.