If you’re reading this on 31 January 2026, you’ve still got time, as long as your return is submitted online by 11:59pm tonight.

And if you don’t make it, don’t panic. Missing the deadline is common, and there are clear steps you can take to limit the damage and get things back under control.

What happens if you file late?

HMRC charge late filing penalties even if you have no tax to pay, so it’s worth submitting as soon as you can. The penalties typically build like this:

• 1 day late: automatic £100 penalty

• 3 months late: £10 per day, up to £900

• 6 months late: extra £300 or 5% of the tax due (whichever is higher)

• 12 months late: another £300 or 5% of the tax due (whichever is higher)

The key point: the fastest way to stop late filing penalties escalating is to submit the return (even if you can’t pay the full bill immediately).

Filing is one deadline. Paying is another.

31 January is also the usual deadline for paying:

• your balancing payment for the previous tax year, and

• (for many people) your first payment on account towards the current year.

If you pay late, HMRC can charge late payment penalties (separate to late filing penalties), typically:

• 5% of unpaid tax at 30 days late

• another 5% at 6 months late

• another 5% at 12 months late

Plus interest on any late-paid tax. As at 9 January 2026, HMRC’s published late payment interest rate is 7.75% (rates can change).

If you can’t pay, act quickly (and you may avoid extra penalties)

If the problem is cash flow rather than paperwork, HMRC may allow you to spread payments using a Time to Pay arrangement.

Important practical points:

• You generally cannot set up Time to Pay until your tax return has been filed.

• HMRC highlight an online option for bills up to £30,000 (subject to conditions), which can often be set up without calling.

• HMRC’s own guidance indicates late payment penalties are not charged where an acceptable Time to Pay arrangement is agreed on or before the first penalty trigger (so speed matters).

Even if you can’t pay in full, paying something now can reduce interest and future penalties.

Missed the deadline? A simple “do this next” checklist

If you’ve not filed on time (or you’re cutting it very fine today), here’s the calm plan:

1. Submit the return as soon as possible
   This is the single best way to stop late filing penalties getting worse.

2. Pay what you can, when you can
   Even a part payment helps reduce interest and the amount exposed to late payment penalties.

3. If you can’t pay in full, explore Time to Pay
   Filing first puts you in the best position to arrange instalments.

4. If you think a penalty isn’t fair, consider an appeal
   HMRC allow appeals against late filing or late payment penalties in appropriate circumstances (for example, a genuine “reasonable excuse”).

5. If you file and later spot a mistake, you can usually amend it
   Online returns can typically be corrected within 12 months of the deadline.

We can help if you’re stuck

If your Self Assessment hasn’t been filed in time, or you’re worried you won’t make it tonight, we’re happy to help.

At Smith Allen Chartered Accountants, we can:

• get your return filed and compliant

• help you understand what you owe (and why)

• support you in arranging instalments with HMRC where appropriate

• advise on next steps if penalties have already been issued

Get in touch:

Email: info@smithallen.uk
Telephone: 07491 770155

No judgement, no lectures, just practical help to get you back on track.