Self Assessment:
the complete guide
You need to file a Self Assessment return if you're self-employed, a company director, earn over £100,000, or have other untaxed income. Register by 5 October if it's your first year, file and pay by 31 January, and a second payment, "payments on account", is often due the same day plus another instalment in July.
Self Assessment catches more people than just the self-employed, and its deadlines come at you from multiple directions across the year: registration, filing, payment, and sometimes a second payment on account. This guide pulls the whole calendar together.
Do you actually need to file?
Self-employment is the obvious trigger, but company directors, landlords, high earners over £100,000, and anyone with untaxed income also generally need to file. See our full breakdown of who must file, including the exceptions people routinely miss.
Registering for the first time
If this is your first year needing to file, you must register with HMRC by 5 October following the end of the tax year, earlier than most people expect. Our registration guide covers exactly how, and what happens if you miss that date.
The deadlines that actually matter
The headline deadline is 31 January, for both filing your return and paying what's due. Less well known is the second payment, "payments on account", often due the same day, which prepays part of next year's tax bill in advance, explaining why your January bill is often bigger than expected. See our payments on account guide and the original full deadline calendar.
What happens if you're late
Late filing and late payment are penalised completely differently by HMRC, and missing 31 January without a plan can escalate quickly. Our penalties guide untangles the two systems, and our missed deadline guide covers exactly what to do if you've already missed it.
If you run a limited company too
Directors often juggle Self Assessment alongside Companies House obligations for the company itself, confirmation statements and annual accounts on a separate schedule entirely. See our Companies House deadlines guide if you're managing both.
In this guide
Who needs to file a Self Assessment return?
The full list of who must file, and the exceptions people miss.
How to register for Self Assessment
The 5 October deadline you can't miss.
Self assessment deadline dates
Every key date for the current tax year, in one place.
Payments on account explained
Why your January bill is bigger than expected.
Self Assessment penalties, explained
Late filing vs late payment, the two separate systems.
What happens if you miss the deadline
What it costs, and the fastest way to limit the damage.
Companies House deadlines
Confirmation statements and company accounts, on their own schedule.
Frequently asked questions
Who needs to file a Self Assessment tax return?
Self-employed people, company directors, those earning over £100,000, landlords, and anyone with untaxed income generally need to file, not just the self-employed.
When is the Self Assessment deadline?
31 January for both filing your return and paying any tax due, with first-time filers also needing to register by 5 October of the same tax year.
What are payments on account?
An advance payment toward next year's tax bill, usually due alongside your January payment and again in July, which is why your Self Assessment bill is often larger than your actual tax liability for the year.
What happens if I miss the Self Assessment deadline?
Late filing and late payment trigger separate penalty systems, both starting with an automatic charge and escalating the longer the return or payment remains outstanding.
Never miss a Self Assessment deadline again
Book a free consultation and we'll handle your registration, filing and deadlines for you.