So you missed the 31 January deadline. Or you filed but now you're not sure if you did it right. Either way — panic is optional. Here's what HMRC actually does, in order.
The penalty timeline
Day 1 late: £100 automatic fine. Doesn't matter if you owe £10 or £10,000. It lands immediately.
3 months late: Daily £10 charges begin. Up to £900 over the next 90 days.
6 months late: 5% of the tax due, or £300 (whichever is higher).
12 months late: Another 5%. Plus potential criminal investigation territory if HMRC thinks you're deliberately avoiding.
What most sole traders don't realise
You can appeal the £100 fine if you have a "reasonable excuse" — serious illness, bereavement, a genuine HMRC system failure. They do accept these. The appeal form is on GOV.UK and takes about 20 minutes.
What you can't do is delay indefinitely hoping they'll forget. They won't. The letters get more formal, then debt collectors get involved.
The actual steps to fix it
- Log into your HMRC online account and check what's actually owed
- File the return, even if you can't pay — penalties stop accruing once you file
- Set up a Time to Pay arrangement if you can't afford the lump sum — HMRC is more accommodating than you'd think
- Appeal any penalties you have grounds for — especially the £100 if you have reasonable excuse
The bit nobody tells you
Filing late is better than not filing. The penalties for non-filing stack up much faster than interest on late payment. Get the return in first, sort the payment second.
If you're confused about what you actually owe — especially with expenses, pension contributions, and whether your home office counts — it's worth working through it methodically rather than guessing and getting it wrong.
I put together a Self-Assessment Recovery Kit for exactly this situation — it's a step-by-step checklist and calculator for UK sole traders who filed late or aren't sure they filed correctly. £9, instant download, HMRC-current for 2024/25.
If you just want the free version: the Self-Assessment Penalties Calculator will show you what you owe in penalties without any signup.
Questions? Drop them below — I check comments on these.
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