On 5 January 2026, HMRC said 5.65 million people still needed to file their Self Assessment return for 2024/25, with the clock ticking towards 31 January 2026 (23:59). That number isn’t just a stat — it’s the reason the last week of January feels like trying to board a budget flight with 200 passengers and one working gate.

Let me tell you a story you’ll recognise.

The night everything goes wrong (and why it keeps happening)

Sam isn’t reckless. Sam is busy. PAYE job. Side consulting. A bit of rental income. A decent spreadsheet that’s “almost ready”.

31 January, 23:17. Sam logs into HMRC. Password reset. Two-factor code… doesn’t arrive. Refresh. Refresh. Lockout.

And here’s the bit most people don’t realise until it hurts: HMRC can hit you with a late filing penalty even if you don’t owe tax — the first £100 is basically the “welcome to February” message.

Sam finally files the next day. Fine. Damage limited… right?

Not quite.

Sam checks the bill and feels sick. It’s not just the balancing payment — there’s another chunk on top: payments on account.

Welcome to the Self Assessment deadline chaos.

First: who actually needs to file? (the 60-second decision tree)

You must file if, in 2024/25, any of these applied:

• self-employed sole trader with over £1,000 gross trading income (before expenses)
• business partnership
• Capital Gains Tax due
• High Income Child Benefit Charge (unless paying it via PAYE)

You may also need to file if you had untaxed income such as:

• rental income
• tips/commission
• savings/investments/dividends
• foreign income

If you’re not sure, HMRC has a formal checker — but the above catches most of the “why am I getting chased?” cases.

The 3 deadlines people confuse (and the one that quietly saves cashflow)

1) Filing deadline (online)

31 January 2026 (23:59) for 2024/25 online returns.

2) Payment deadline

Also 31 January 2026 (23:59) for the tax you owe (and usually more — see payments on account).

3) “Pay through PAYE” option (coding out)

If your bill qualifies and you want it collected via your PAYE tax code, the online return typically needs to be filed by 30 December 2025 (23:59). Miss that, and you’re paying another way.

The penalty timeline (late filing vs late payment)

People mash these together. HMRC doesn’t. They stack.

Late filing penalties (return submitted after 31 Jan)

• £100 initial penalty
• after 3 months: £10/day up to £900
• after 6 months: additional 5% of tax due or £300 (whichever is higher)
• after 12 months: another 5% or £300

Late payment penalties (tax paid after 31 Jan)

• 5% of unpaid tax at 30 days, 6 months, 12 months, plus interest

This is why “I filed but I can’t pay” still needs a plan.

Why January hurts more than expected: payments on account

This is the trap that makes grown adults open banking apps like they’re horror films.

Payments on account are advance instalments towards your next tax bill, due 31 January and 31 July.

You generally have to pay them unless:

• last year’s tax bill (the SA amount) was under £1,000, or
• you already paid 80%+ of your tax at source (e.g., via PAYE coding)

And the nasty surprise: the 31 January amount often includes:

• the balancing payment for 2024/25, plus
• the first payment on account for 2025/26

If your income is dropping, you can apply to reduce payments on account — but underestimate and you risk interest later.

HMRC systems/helplines failing: what to do so you don’t get burned

If HMRC services glitch when you’re trying to comply, you need an evidence trail.

HMRC explicitly recognises that issues with HMRC online services (or your computer/software failing while preparing an online return) may count as a reasonable excuse, but you still need to submit/pay as soon as you’re able.

Do this in real time:

• screenshot error messages (include the device clock if possible)
• record timestamps (even a notes app log is better than memory)
• keep confirmation emails / submission receipts
• if you can’t submit online, attempt alternative routes (different browser/device) and document attempts

This won’t magically erase penalties — but it gives you something solid if you need to appeal.

“I can’t pay” — the correct way to use Time to Pay

If you can’t clear the bill by 31 January, don’t hide. File first, then act.

HMRC is actively pushing Time to Pay arrangements and says that, for Self Assessment bills up to £30,000, many people can set up an instalment plan online without speaking to HMRC — but you can’t set it up until the return is filed.

Practical tip: if cash is tight, focus on filing before the deadline (to stop the late filing penalty snowball), then get the payment plan in motion.

If you’re due a refund: realistic expectations (and how to chase properly)

Here’s the uncomfortable truth: refunds are a hot topic because people are reporting long delays — including cases where repayments take many months, even over a year.

Two technical points that catch people out:

1. If you have tax due in the next 45 days (often because of a payment on account), HMRC may offset instead of refunding cash.
2. Your online account may show the refund as “pending” — meaning it exists, but still needs approval and payment.

Chasing, properly (no drama, just leverage):

• check your SA statement for offsets due within 45 days
• confirm bank details are correct (and consistent with the account profile)
• keep a paper trail of dates, amounts, and screenshots of “pending” status
• if it becomes excessive, escalate via HMRC complaints route (and be ready with the timeline)

The 7 mistakes that trigger penalties (and the fast fixes)

1. You confuse “file” with “pay”. Fix: treat them as two separate projects. Filing stops one penalty track; paying stops the other.
2. You leave login/access until the final night. Fix: test your Government Gateway access now — password reset at 11pm is a self-inflicted wound.
3. You forget payments on account and budget for only the balancing payment. Fix: check whether POAs apply (the £1,000 / 80% rule), then ring-fence the January + July hits.
4. You miss the PAYE coding-out deadline without realising it existed. Fix: if you want tax collected through PAYE, the date is usually 30 December.
5. You “can’t pay” and do nothing. Fix: file, then Time to Pay — many can do this online for up to £30k.
6. You rely on “HMRC was down” but keep no evidence. Fix: screenshots + timestamps. HMRC service issues can support a reasonable excuse — but only if you can show what happened.
7. You expect a refund, but it’s offset (or stuck pending) and you don’t check the statement. Fix: review the 45-day offset rule and the “pending” status meaning before you panic-refresh your bank app.

“Do this tonight” action plan (45 minutes, max)

• 10 mins: confirm you actually need to file (use the list above)
• 10 mins: regain access: Government Gateway login, 2FA, recovery methods
• 15 mins: gather numbers: PAYE income, interest/dividends, rental totals, pension/Gift Aid, any foreign income
• 5 mins: check if payments on account will apply and what that does to January’s bill
• 5 mins: decide the payment route: pay in full vs Time to Pay (but file first either way)

Mail: angelo@vectigalistax.co.uk 

Disclaimer: this is general information, not tailored advice. Self Assessment can get technical fast (especially with foreign income, CGT, remittance/FIG, residence issues, or multiple employments).