You file a UK self assessment return if you have income HMRC doesn’t already tax at source — which, for most company directors, means the moment you start taking dividends. You register for a Unique Taxpayer Reference (UTR), file online by 31 January, and pay what you owe by the same date. Late, and you get an automatic £100 penalty even if you owe nothing.
The thing to hold onto from the start: self assessment is your tax return as a person. It is not your company’s Corporation Tax return. Founders blur the two constantly and end up either filing the wrong thing or missing one entirely. Here’s who must file, how to register, the deadlines that matter, and what changes if you’re a non-resident director.
Who actually has to file
Self assessment is HMRC’s way of taxing income that isn’t already taxed through PAYE. You’re in the system if any of these apply.
There’s an old myth that every UK company director must file self assessment. Not so — it’s the income that triggers it, not the title. A director paid only a small salary under PAYE with no dividends may not need to file. But take dividends out of your company beyond the allowance, and you almost certainly do.
That dividend point is the one that catches founders. You set up the company, it makes a profit, you pay yourself a dividend — and now you personally owe tax on that dividend, separately from the Corporation Tax the company already paid on its profit.
Registering and getting your UTR
Before you can file, HMRC has to know you exist as a self assessment taxpayer. That means registering and getting a UTR — your Unique Taxpayer Reference, a 10-digit number that tags everything you file.
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Register for self assessment
Tell HMRC you need to file, through GOV.UK. You’ll set up a Government Gateway account in the process. The deadline to register is 5 October after the end of the tax year you need to report.
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Receive your UTR by post
HMRC sends your UTR in the post. This is the slow step, and the one that ambushes non-residents — international post takes weeks. Register early; don’t start in January.
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Activate your online account
HMRC posts an activation code for online services. Again, by post. Once activated, you can file online and see what you owe.
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File the return and pay
Complete the return for the relevant tax year, declaring your income and reliefs, then pay the tax due. The system calculates the bill as you go.
Everything in registration moves at the speed of the postal service: the UTR, then the activation code, both to your address abroad. A non-resident who waits until January to register will miss the 31 January filing deadline simply because the numbers haven’t arrived. Register as soon as you know you’ll need to file.
The deadlines that matter
The UK tax year runs 6 April to 5 April. The deadlines hang off the year that just ended.
| Deadline | What's due |
|---|---|
| 5 October | Register for self assessment (if you're new to it) |
| 31 October | Paper return deadline |
| 31 January | Online return deadline and tax payment |
| 31 January | First payment on account (if applicable) |
| 31 July | Second payment on account (if applicable) |
Almost everyone files online, so 31 January is the date to burn in: file and pay by then. Note the same date carries the tax payment — filing without paying still leaves you with interest and possible penalties on the unpaid amount.
Payments on account
If your tax bill is large enough, HMRC asks you to pay next year’s tax in advance, in two instalments called payments on account. Each is half of your previous year’s bill, due 31 January and 31 July. The first time it happens it stings: in one January you can owe last year’s full bill plus the first instalment of this year’s — effectively 150% of a normal bill. It’s not an extra tax, it’s prepayment, and it evens out, but plan your cash flow for it.
Non-resident directors with UK dividend income
This is where it gets genuinely case-by-case, and where guessing is expensive in both directions. If you live outside the UK and take dividends from your UK company, whether and how much UK tax you pay depends on your tax residence and any double-taxation treaty between the UK and the country you live in.
Some non-resident founders assume living abroad means the UK can’t tax their dividends; others assume they owe full UK tax on everything. Both can be wrong. The disregarded-income rules and treaty relief make this one of the areas where a short conversation with someone who knows your country pays for itself. See also UK Ltd vs US LLC if you’re still choosing a structure, and non-resident UK VAT if you’re selling into the UK.
Self assessment is not your company’s Corporation Tax
The cleanest way to keep this straight: there are two taxpayers, you and the company, and each files its own return.
| Self assessment | Corporation Tax (CT600) | |
|---|---|---|
| Who's the taxpayer | You, the individual | The company |
| Taxes | Your salary, dividends, other income | The company's profit |
| Filed with | HMRC | HMRC |
| Main deadline | 31 January (online) | 12 months after year end |
| Triggered by | Untaxed income / dividends | The company making profit |
The company pays Corporation Tax on its profit and files a CT600. Then, when you extract money as a dividend or salary, you pay personal tax on that through self assessment (salary is taxed under PAYE; dividends usually land on the self assessment return). Same HMRC, two completely separate filings. Doing the company’s Corporation Tax does nothing for your personal return, and vice versa.
Penalties for filing late
The penalties are automatic and they stack, so don’t drift past 31 January.
The first £100 is charged automatically once the deadline passes, whether or not you owe anything. Filing a nil return a day late still costs you £100. For a non-resident, the realistic way to miss it isn’t laziness — it’s not registering early enough to get the UTR in time. Treat registration as the deadline that matters.
If your circumstances changed and you no longer need to file, tell HMRC and get the notice withdrawn — otherwise the obligation, and the penalties, keep running.
We handle UK personal self assessment and the company’s Corporation Tax together for cross-border founders, so the two returns line up, the dividends are reported correctly, and nothing gets filed late because a UTR was stuck in the post.
File your UK self assessment right
See UK tax filing →
