Reacting to: Improved Self Assessment registration service launched (gov.uk (HMRC)) →
HMRC launched a rebuilt Self Assessment registration service this morning. Most of the announcement is the sort of thing that reads as housekeeping — pre-populated forms, a save-and-return button, a confirmation email when you are done. One line in it is not housekeeping at all, and it changes the sensible timing of the whole job.
People registering through the new route get their Unique Taxpayer Reference in their online account within 72 hours, instead of waiting up to 15 days for it to come in the post. You cannot file a tax return without a UTR. Until today, leaving registration until mid-January meant genuinely risking the 31 January filing deadline on Royal Mail. That risk has largely gone.
My view: take the improvement, then ignore it. The point of registering by 5 October 2026 was never the postal wait — it is that 5 October is a statutory obligation with a penalty attached, and the penalty is a percentage of your tax, not a flat fee. More than 640,000 people registered for Self Assessment in the 12 months to 31 March 2026, on HMRC's own count. A good number of them will have done it in January, and some of them paid for that.
Who this actually catches
HMRC's published triggers for a 2025/26 return, if you are not already registered, are these:
- You are newly self-employed with gross income over £1,000. Gross, not profit. Turnover of £1,400 with £900 of costs still counts.
- You earned under £1,000 and want to pay voluntary Class 2 National Insurance to protect your State Pension and certain benefits.
- You became a new partner in a business partnership.
- You received any untaxed income over £2,500 — rent, dividends outside a wrapper, freelance work on the side.
The £1,000 trading allowance is what takes the smallest side incomes out of the system entirely: earn less than £1,000 in the year and you do not need to declare it or pay tax on it.
The obligation itself is not an HMRC preference. Its failure-to-notify factsheet puts it plainly: where your profits from self-employment first make you chargeable to tax, you must tell HMRC within six months of the end of that tax year. Six months after 5 April 2026 is 5 October 2026, which this year falls on a Monday.
Worked example: what a first Self Assessment bill really looks like
Illustrative, using published 2025/26 rates. A sole trader who started trading in the 2025/26 year, made £38,000 of profit, and has no other income.
| Item | How it is worked out | Amount |
|---|---|---|
| Income Tax | (£38,000 − £12,570) × 20% | £5,086.00 |
| Class 4 National Insurance | (£38,000 − £12,570) × 6% | £1,525.80 |
| Tax for 2025/26 | £6,611.80 | |
| First payment on account | Half of £6,611.80 | £3,305.90 |
| Due 31 January 2027 | £9,917.70 |
That last row is the one nobody is ready for. Because the bill is over £1,000 and none of it was collected at source, HMRC also asks for a payment on account towards next year on the same day — so the first January is one and a half years of tax in a single payment, with the second £3,305.90 following on 31 July 2027. We set the mechanics out in full in the July payment deadline explained.
Register on 5 October and you know that £9,917.70 figure by mid-October. Register in January and you find it out roughly a fortnight before it is due.
What registering late costs, in money
Here is the part worth being precise about, because it is more forgiving than most people assume and much harsher than the rest assume.
Registering after 5 October is only penalised if you also fail to pay in full by 31 January. GOV.UK says the failure-to-notify penalty is based on the amount still left to pay, and arrives within 12 months of HMRC receiving your return. Register late, file, pay everything on time — no penalty.
Miss both, and the penalty is a share of the tax. HMRC's factsheet sets the ranges for a non-deliberate failure at 0% to 30% where you disclose it yourself before HMRC finds it, and 10% to 30% where HMRC gets there first. Deliberate failures run to 70%, and deliberate and concealed to 100%. On the same £6,611.80 bill above, and assuming nothing was paid by 31 January:
| Charge | Basis | Amount |
|---|---|---|
| Failure to notify, prompted | 10%–30% of £6,611.80 | £661.18 – £1,983.54 |
| Late filing, initial | Fixed | £100.00 |
| Late payment, 30 days | 5% of tax unpaid | £330.59 |
| Late payment, 6 months | 5% of tax unpaid | £330.59 |
| Total penalties | £1,422 – £2,745 |
That is 21.5% to 41.5% on top of the tax, before interest, and the failure-to-notify slice of it is the only one you can still make disappear entirely by telling HMRC yourself first. The gap between the 0% floor for an unprompted disclosure and the 10% floor for a prompted one is £661.18 on this bill. It is bought with a phone call.
The £182 nobody claims
The second trigger on HMRC's list is the one people skip, and it is the only entry there that puts money back in your pocket rather than taking it out.
If your self-employed profits for 2025/26 were under the £6,845 Small Profits Threshold, you owe no National Insurance at all. But you can register anyway and pay voluntary Class 2 at £3.50 a week — £182 for the year — which buys a qualifying year towards your State Pension. Leave it, and filling that same gap later with voluntary Class 3 costs £17.75 a week, or £923 for the year.
£741 of difference for the identical qualifying year, and the cheap version is only available while you are inside Self Assessment for that year. A quiet first year of trading is exactly when people decide registering is not worth the bother.
Two other dates this month, and neither is 5 October
20 September 2026, 23:59 — the Winter Fuel Payment opt-out. This one is 11 days away. If you received the Winter Fuel Payment and your total income is over £35,000, you pay it back through Self Assessment, due 31 January 2027. HMRC is pre-populating it into 2025/26 online returns where it can, and you should check and add it manually if it is not shown. If you would rather not receive it at all, the opt-out closes at 23:59 on 20 September, or midday on 19 October 2026 for the Pension Age Winter Heating Payment in Scotland.
31 October 2026 — the paper filing deadline. Paper filers get three months less than everyone else, and must add the Winter Fuel Payment themselves.
Two more from the same announcement, both easy to miss. Around 300,000 people will now find their Child Benefit figures pre-filled on the return, which matters if adjusted net income is over £60,000 and the High Income Child Benefit Charge applies — that is 1% of the Child Benefit clawed back for every £200 of income above the threshold, and all of it at £80,000. And if you are already registered but did not file for 2024/25, you have to reactivate the account before you can file this year. Signing up to Making Tax Digital for Income Tax does not replace the return either — HMRC confirms MTD customers still file a Self Assessment return and pay by 31 January 2027.
What is still uncertain
The new route is for individuals only. HMRC is explicit that the improved service is for customers with a Personal Tax Account, and that agents must continue to use the existing processes — forms CWF1 and SA1. It has not said whether or when the agent route gets the same treatment. If we register you, expect the old timings, which is one more reason to start now rather than in January.
The 72-hour figure has not met January yet. It is HMRC's own service standard for a service launched today, and January is when the volume arrives. Treat it as a good reason to register early, not a reason to leave it late.
The Budget on 28 October will not change this bill. The 2025/26 rates are set and the year has closed. Anything announced in October affects 2026/27 onwards, so nothing you hear that week alters the £9,917.70 due on 31 January 2027.
Four things to do this week
- Check whether you need to file at all. HMRC's free tool takes about two minutes: GOV.UK: check if you need to send a Self Assessment tax return.
- If you do, register now, not on 5 October. Start at GOV.UK: register for Self Assessment. You will need a Personal Tax Account, reachable with Government Gateway or GOV.UK One Login details.
- If you have stopped, tell HMRC. Do not assume silence ends it — a return will still be expected and a non-submission penalty issued. Use GOV.UK: if you no longer need to send a return.
- If you are over State Pension age with income above £35,000, decide on the Winter Fuel Payment before 20 September. Keeping it is fine — it just comes back out of the January bill.
None of this is difficult. It is just unforgiving about dates, and the cost of getting it wrong scales with how well the year went. Registering people, working out the real number and getting it filed early is ordinary work for our Self Assessment service, and it sits inside the accountancy packages most of our sole trader clients are on. If you are not sure whether this year caught you, tell us what happened and we will come back to you the same working day.
Sources: HMRC, "Improved Self Assessment registration service launched", published 9 September 2026; failure-to-notify time limits and penalty ranges from HMRC factsheet CC/FS11, updated 19 March 2026; late filing and late payment penalties from GOV.UK Self Assessment penalties; payments on account from GOV.UK; 2025/26 National Insurance thresholds and Class 2 and Class 3 rates from HMRC rates and allowances; High Income Child Benefit Charge thresholds from GOV.UK. Personal allowance £12,570 and basic rate 20% for 2025/26. Figures correct at 9 September 2026.