Anyone who started earning self-employed income in the 2025/26 tax year has until 5 October 2026 to notify HMRC. Nobody sends a reminder, the practice does not do it for you, and the return this produces is the one that decides your Making Tax Digital start date.
Article · 11 August 2026
Dentistry has an unusual entry point into self-employment. Foundation training is a salaried post with PAYE, National Insurance and a payslip that arrives already taxed. Then, usually in the autumn, you move to an associate post and every one of those mechanisms stops at once. Nothing is deducted for income tax. Nothing is reported to HMRC on your behalf. And the practice, which is your customer rather than your employer, has no obligation to tell anyone you exist.
The obligation is yours, and it has a date on it. If you had self-employed income in the tax year that ran from 6 April 2025 to 5 April 2026, you must notify HMRC that you are chargeable to tax by 5 October 2026. That is eight weeks away, and the practical deadline is sooner, because registration is a paper-speed process at the far end.
Not only new associates, and that is where it goes wrong:
The two beliefs that cause most late registrations are that a small profit means no obligation, and that the practice or the NHS has already reported you. Neither is right. The test is whether you are chargeable to tax, not whether you feel established, and the £1,000 threshold is measured on gross receipts before a single expense.
Registering for self assessment as a self-employed person is done online through the CWF1 service on GOV.UK. You need a Government Gateway account first, and if you have never had one, setting it up is its own small errand. Registration produces a Unique Taxpayer Reference — the ten-digit UTR that every subsequent filing hangs off — and HMRC posts it to you. Allow two to three weeks for it to arrive, then a further wait for the activation code that lets you actually use the online account.
If you already have a UTR from a previous year, you still need to register the self-employment itself. The UTR identifies you; CWF1 tells HMRC there is now a trade to report and starts your Class 2 National Insurance record. People who filed a return once as a student, or who registered for the high income child benefit charge, routinely assume they are already covered and are not.
Take a dentist who finished foundation training on 30 September 2025 and started an associate post the next day. The figures below are illustrative, but the shape is the ordinary one.
Trading profit is £44,000 less £2,600 less £4,000, so £37,400. Superannuation is relieved separately, which is the point covered in the next section. Total income for the year is £18,000 plus £37,400, less the £4,100 of pension relief, giving £51,300. Take off the personal allowance of £12,570 and £38,730 is taxable: £37,700 in the basic rate band at 20% is £7,540, and the remaining £1,030 at 40% is £412. Income tax for the year is £7,952, less the £1,086 already paid under PAYE, so £6,866 is outstanding.
Class 4 National Insurance is charged at 6% on trading profit between £12,570 and £50,270. On £37,400 that is 6% of £24,830, or £1,489.80. Class 2 costs nothing here: since April 2024 profits above the small profits threshold — £6,845 for 2025/26 — are treated as though Class 2 had been paid, so the state pension year is credited without a payment.
The balancing payment due on 31 January 2027 is therefore £8,355.80. That is not the bill. Because it exceeds £1,000 and less than 80% of the year's tax was collected at source — £1,086 out of £9,441.80, around 11% — payments on account for 2026/27 are triggered as well. Each is half the balancing payment, £4,177.90, and the first falls due on the same day.
Notice that the £4,100 of superannuation reduced the income tax calculation but not the Class 4 National Insurance one. That is deliberate, and it is the single most common error in a self-prepared dental return.
Contributions deducted from your NHS pay statements are member pension contributions, not business expenses. HMRC's guidance for doctors and dentists treats both the employee and employer elements paid by a self-employed practitioner as relievable member contributions. Put them in the expenses column and you reduce trading profit — which cuts your Class 4 National Insurance by 6% of the contribution, relief you are not entitled to, and misstates the profit figure that a lender, a practice vendor or a mortgage broker will later read off your accounts. Code superannuation to its own account, outside trading expenses, from the first month. Our NHS pension guide covers what those deductions are buying you.
The penalty for failing to notify is tax-geared. It is a percentage of the potential lost revenue, which for income tax is defined as the tax still unpaid on 31 January following the tax year — 31 January 2027 in this case. Two consequences follow, and they point in opposite directions.
The reassuring one: if you register late but get the return filed and the tax paid by 31 January 2027, the potential lost revenue is nil, so a percentage of it is also nil. Missing 5 October is not, by itself, an automatic fine.
The unreassuring one: the percentages are set by behaviour and by who moved first. For a non-deliberate failure disclosed within twelve months of the tax falling due, an unprompted disclosure can be reduced to 0%, while a prompted one — where HMRC contacted you before you contacted them — carries a minimum of 10%, rising to a 30% maximum. A deliberate failure starts at 20% unprompted and runs to 70%. Going to HMRC before HMRC comes to you is worth real money, and it is the only part of this you control once the date has passed.
Separately, late filing and late payment penalties run on their own timetable from 31 January, and those are not discretionary.
Making Tax Digital for Income Tax began on 6 April 2026 for people whose 2024/25 return showed qualifying income above £50,000. The threshold drops to £30,000 from 6 April 2027, and the return HMRC tests for that is the 2025/26 one — the return this registration creates.
Qualifying income is gross income from self-employment and property, before expenses. In the example above it is £44,000, from six months of trading, so that dentist is inside MTD from April 2027 and will be filing quarterly updates from their second full year. The foundation training salary does not count towards it, because employment income is outside the test. Anyone who registers late and files a rushed return risks discovering the obligation with no bookkeeping system behind it. Our Making Tax Digital guide for dentists sets out what the quarterly updates involve.
None of this is difficult; it is simply invisible until it is late, because no payslip, practice manager or NHS system prompts it. If you started as an associate during 2025/26 and nobody has walked you through the first year yet, our first-year associate money checklist is the place to start, and the dental tax calendar has the rest of the year's dates. If you would rather hand the whole sequence to someone who does it every autumn, have a conversation with us before the deadline picks the timetable for you.
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Almost certainly yes. The test is gross receipts, not profit, and the trading allowance sets the line at £1,000 of gross income before any expenses. Two months of associate work will clear that comfortably, so the obligation to notify HMRC by 5 October applies even if the profit after lab fees, indemnity and GDC retention is modest, and even if no tax ends up being payable at all. Registering also starts your National Insurance record for the year, which matters for the state pension. The one genuine exception is gross receipts of £1,000 or less with no other reason to file, and a part-time associate rarely sits there.
No, and this is the assumption that produces the worst January surprises. Superannuation is a pension contribution, not income tax, and it buys you scheme benefits rather than settling anything with HMRC. Nothing at all is deducted for income tax from associate payments, so a pay statement showing a deduction can read like a payslip while doing none of a payslip's work. Treat superannuation as a member pension contribution relieved through your tax return, keep it out of your business expenses, and set aside tax separately as you go. The deduction reduces your income tax bill; it does not pay it.
Register straight away and disclose it yourself rather than waiting to be asked. The failure to notify penalty is a percentage of the tax still unpaid on the 31 January following the tax year, so if you file and pay promptly the potential lost revenue can be small or nil. The percentage depends on behaviour and on who raised it first: a non-deliberate failure disclosed unprompted within twelve months can be reduced to nil, while the same failure disclosed after HMRC makes contact starts at 10% and can reach 30%. Late filing and late payment penalties run separately, so speed genuinely reduces what you pay.
Yes, for the self-employment itself. Your UTR identifies you as a taxpayer, but it does not tell HMRC that you have started a trade, and the notification obligation attaches to the new source of income rather than to you as a person. Completing CWF1 registers the self-employment, opens your Class 2 National Insurance record and makes sure a return is issued for the right year. Keep the UTR you already have — you will not be given a second one. The people caught by this are usually those who filed once for a student job or for the high income child benefit charge and assumed the account covered everything.
For most new associates, yes. The Making Tax Digital threshold falls to £30,000 of qualifying income from 6 April 2027, and HMRC tests that against the 2025/26 return. Qualifying income is gross income from self-employment and property before expenses, so an associate with even half a year of receipts will usually be over the line and inside the regime from April 2027. Foundation training salary does not count, because employment income sits outside the test. The practical implication is that the bookkeeping habits you set up for your first return are the ones you will be filing from quarterly, so it is worth getting the structure right at the start.
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