Self Assessment Deadlines, Explained Simply

Self Assessment involves more than one deadline, and it's easy to assume they're all the same date. They're not — and missing any of them can mean a penalty, even if the others were done on time. Here's the general shape of it (always double-check current dates directly with HMRC, since these can be adjusted).

Registering for Self Assessment

If this is your first time needing to file — for example, you've just become self-employed, started renting out a property, or had a change in income — you usually need to register with HMRC by 5 October following the end of the tax year in which the change happened. This is easy to miss because it doesn't feel urgent at the time.

Filing your return

For most people, the deadline to file an online return is 31 January following the end of the tax year (which runs 6 April to 5 April). Paper returns have an earlier deadline, usually 31 October. Filing online is the far more common route for most individuals and small businesses these days.

Paying what you owe

The deadline to pay any tax owed is also 31 January — the same date as the online filing deadline. Some people also need to make a “payment on account” towards the following year's bill, split between 31 January and 31 July. This trips people up regularly, since it means the January bill can be larger than expected.

Why leaving it late causes problems beyond the deadline

Aside from penalties, filing at the last minute doesn't leave much room to deal with anything unexpected — a missing document, a question about what counts as an allowable expense, or simply not having enough information gathered together. Getting support earlier in the year, even just to understand what you'll eventually need, tends to make January far less stressful.

If you're not sure whether you need to register, or you're already behind and need to catch up, that's a completely normal reason to get in touch with a professional — it doesn't need to be sorted out alone.