Every tax season, the same thing happens: someone means to sort their self assessment in good time, life gets busy, and suddenly it’s the last week of January. If that sounds familiar, this article covers the dates that actually matter and what happens if one slips past you.
The dates that matter
For most people filing online, there are two dates worth writing down. The registration deadline applies if this is your first time filing — HMRC needs advance notice that you’ll be submitting a return at all. The filing and payment deadline is the one most people know about, and it’s also the date any tax owed needs to be paid by, not just declared.
A third, quieter deadline applies to anyone who wants to pay a tax bill through their PAYE tax code rather than as a lump sum — that one falls earlier in the year and is easy to miss because it’s rarely mentioned outside accounting circles.
What actually happens if you miss the deadline
HMRC’s penalties start the moment the deadline passes, not weeks later. An initial fixed penalty applies immediately, followed by daily penalties if the return is still outstanding after three months. Miss it by six months, and a further penalty is added on top of what’s already accrued — and that’s before interest on any unpaid tax is factored in.
The part that catches people out is that these penalties apply even if you don’t owe any tax. Filing late is treated as a separate issue from paying late, and HMRC penalises both independently.
If you’ve already missed it
The single most useful thing you can do is file as soon as possible rather than waiting until the situation feels more “sorted.” Penalties are calculated based on how late the return is, so every week of delay adds to the bill.
How to avoid this next year
Getting your accountant the relevant records a few months early, rather than a few days early, turns filing from a scramble into a formality. This is exactly the kind of deadline management we handle for self assessment clients.
