Can you still file Self Assessment in the last two weeks of January?
Yes. The online Self Assessment deadline for the 2025/26 tax year is 11:59pm on 31 January 2027, and you can file right up to it through your HMRC online account, with or without an accountant. The clock does not care whether you start on the first of January or the thirtieth. What matters is that the return is submitted and the tax is paid, or a payment plan is in place, before midnight closes the door.
The paper route has already gone by then. Paper returns for 2025/26 were due by 31 October 2026, so from November onward the only option is filing online, which is what the vast majority of people use anyway. HMRC publishes the full set of dates in its Self Assessment deadlines guidance.
This guide is written by LOYALS, a King's Cross firm of accountants and business consultants that files Self Assessment returns and handles personal tax for business owners across London. We do the late-January scramble every year, so most of what follows is the running order we actually use when someone calls with days to spare. If you want the calm version, our companion piece on why filing in September beats January makes the case for never being here again.
One more framing point before the practical steps. A late return and late tax are two different problems with two different penalty systems. You can be on time for one and late for the other. That distinction runs through everything below, and it is the single thing most people get wrong when panic sets in.
The three things you actually need before you can file
To file online you need exactly three things: your Unique Taxpayer Reference (UTR), your Government Gateway user ID and password, and your income and expense figures for the tax year that ran from 6 April 2025 to 5 April 2026. Get those in front of you and the return itself is usually an hour or two of work, not the mountain it feels like from the sofa.
Your UTR is the ten digit number HMRC uses to identify you. It sits on any previous tax return, on your HMRC online account, and on old letters headed Self Assessment. If you have filed before, you already have one and it never changes. The Government Gateway login is separate: a user ID and password you set up the first time you registered for online services. And the figures are simply your income by source, your allowable expenses, and anything already taxed at source, like PAYE salary or bank interest.
Here is the part that saves people every year. If a figure is not final, you are allowed to enter a considered estimate, tick the box on the return that says it contains provisional or estimated figures, and correct it later. A missing bank statement or an accountant who has not sent your rental summary is not a reason to blow the deadline. File a sensible provisional number now, then amend the return within twelve months once the paperwork lands.
The decision tree below is the one we walk clients through on the phone. It sorts the genuinely urgent blocker from the ones you can work around in an evening.
What to do if you have lost your login or never registered
Recovering a forgotten Government Gateway login takes minutes, but getting a UTR you have never had takes up to ten working days, so this is the one blocker to deal with today rather than tomorrow. Access is the part of the job with a queue behind it, and the queue does not move faster because you are in a hurry.
Lost your user ID or password? Use the recovery links on the HMRC sign in page. As long as you can still receive email and text codes, most people are back into their account inside fifteen minutes. Keep the details somewhere safe this time, because you will want them again next January.
Never registered at all? That is the serious one. If 2025/26 is your first year of untaxed income, you were meant to register by 5 October 2026 under HMRC's register for Self Assessment guidance. You can still register late, but HMRC posts your UTR out, and it can take up to ten working days to arrive. Register in the third week of January and it may simply not reach you in time. Register anyway, the same day you realise, because acting promptly and filing the moment the reference lands is what limits the penalties and gives you a reasonable excuse to lean on. Leaving it late is not itself a reasonable excuse, so do not wait.
People caught by this are often new landlords, side-hustlers who crossed the £1,000 trading allowance, and directors who took dividends for the first time. If any of those is you, our plain-English walkthrough of how much tax you pay when self-employed will tell you whether you even needed to register, and roughly what the bill looks like.
What if you cannot pay the tax by 31 January?
File anyway. The penalty for filing late and the penalty for paying late are two separate charges, so submitting the return on time stops the £100 fixed penalty even if you cannot pay a penny of the tax yet. Refusing to file because you are worried about the bill is the most expensive mistake in the whole process, because it triggers penalties that had nothing to do with the money you owe.
Once the return is in, deal with the tax through a payment plan. If you owe £30,000 or less, you can usually set up a Time to Pay instalment arrangement online, within 60 days of the deadline, without phoning anyone. A plan that you keep to stops the 5 percent late payment penalties from being charged, which is a real saving. Interest still runs on the outstanding balance, so the sooner it clears the better, but the arrangement takes the penalty risk off the table. HMRC sets out the options in its guidance on what to do if you cannot pay your tax bill on time.
Watch the payments on account trap while you are here. Your 31 January bill is often the balancing payment for one year plus the first payment on account for the next, so the number can be larger than the tax on your profit alone. If your income has genuinely dropped, you can apply to reduce the payments on account rather than borrow to fund a figure based on a better year. Get that judgement wrong in either direction and it costs you, which is exactly the sort of call worth a five-minute conversation.
What a missed 31 January actually costs
Miss the filing deadline and £100 is charged the next day, even if you owe nothing or have already paid the tax. That fixed penalty is automatic and it does not scale with your bill, so a nil return filed on 1 February costs the same £100 as a complicated one. After that, the charges climb, and they climb on two separate tracks.
The late filing penalties come first. Three months late, HMRC adds £10 a day for up to 90 days, another £900 on top of the £100. At six months there is a further penalty of £300 or 5 percent of the tax due, whichever is greater, and the same again at twelve months. HMRC's penalties guidance sets out each stage. So a return that is simply never filed can reach £1,600 in filing penalties alone, before a single pound of the actual tax is considered.
The late payment penalties run alongside, on the tax itself. Tax still unpaid 30 days after the deadline attracts a 5 percent surcharge, with another 5 percent at six months and a third 5 percent at twelve months. On top of all of it, interest accrues daily from 1 February at 7.75 percent a year, the rate in force since 9 January 2026, which HMRC publishes in its interest rates for late and early payments. The chart below shows how it stacks up on a fairly ordinary £6,000 bill left a full year.
The lesson is not to frighten anyone. It is that the £100 and the £900 daily penalties apply purely for filing late, so they are entirely avoidable by getting the return in, even when the money is a struggle. Sort the filing, then handle the payment calmly through a plan.
DIY, a generalist or a specialist: what actually differs in the last two weeks
In the final fortnight the difference between the three routes is not really price, it is whether someone picks up the phone and whether they can file a safe provisional return before midnight. Plenty of people file their own return happily every year, and if your affairs are simple you may not need anyone. It is the awkward last-minute cases, a lost login, a missing figure, a bill you cannot pay, where having a specialist on the end of the phone changes the outcome.
Here is how the three common last-minute routes compare while the 31 January clock is running:
| What you need in the last two weeks | DIY / software | Generic accountant | LOYALS specialist |
|---|---|---|---|
| Reachable in the last two weeks of January | ● Always on, no help | ✗ Often fully booked | ✓ Mon to Sat 10am to 7pm |
| Files a safe provisional return when a figure is missing | ✗ You self-judge it | ● If they take you on | ✓ Built into how we file |
| Handles a missing UTR or a Gateway lockout | ✗ | ● | ✓ Guided the same day |
| Sets up a Time to Pay plan if you cannot pay | ✗ You arrange it alone | ● | ✓ Set up with you |
| Spots reliefs and expenses you would miss under pressure | ✗ | ● | ✓ Checked before we submit |
| Fixed fee agreed before any work starts | ✓ Software cost only | ● Rush or hourly common | ✓ Quoted in writing first |
This is why owner-managers who leave it late tend to call a specialist rather than gamble on the software or a fully-booked generalist.
What to do now, in order
The fastest path through the last two weeks is to deal with access first, figures second, and payment last. Do it in that order and nothing blocks you at the final hour.
- Check your access today. Find your UTR, sign into your Government Gateway account, and reset the password now if it does not work. If you have never registered, register the same day, because the UTR posts out over up to ten working days.
- Pull your figures together. Income by source, allowable expenses, and anything already taxed like salary or interest. Estimate anything you cannot finalise and note what still needs checking.
- File the return, provisional if you must. Enter your best figures, tick the provisional box for any estimates, and submit before 31 January. This alone kills the £100.
- Sort the payment separately. Pay what you can, and set up a Time to Pay plan for the rest if you owe £30,000 or less. That stops the 5 percent surcharges.
- Reduce payments on account if income has genuinely fallen. Do not borrow to fund a payment on account based on a better year than the one you are in.
- Amend later if you filed provisionally. You have until twelve months after the deadline to replace estimates with final figures.
If you would rather not spend the last two weeks of January doing any of this, you can hand the whole thing over. LOYALS is a team of London accountants and business consultants who file Self Assessment returns and sort the tax alongside, and we keep the door open on Saturdays precisely because deadlines do not fall on convenient days. For the ongoing quarterly picture that is coming for many, our note on the MTD quarterly update due 7 November 2026 explains what changes next.