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Self Assessment vs Company Tax Return: The Difference

Updated 10 Jun 2026

Self Assessment is a personal tax return. A Company Tax Return (the CT600) belongs to a limited company. They go to HMRC separately, on different deadlines, and one never stands in for the other: a sole trader files only Self Assessment, a limited company always files a CT600, and a company director may end up filing both. Here's how the two returns differ and which ones apply to you.

What is Self Assessment?

Self Assessment is how individuals report income that isn't taxed automatically. If you're a sole trader earning more than £1,000 of gross trading income in a tax year, you register (by 5 October after the end of that tax year) and then file a return each year — online by 31 January, or 31 October on paper. The tax you owe is due by 31 January too, with a second instalment on 31 July where payments on account apply.

The return is yours, personally. It covers your trading profits and any other personal income, and it follows the tax year (6 April to 5 April). Sole trader accounts covers the full picture.

What is a Company Tax Return?

A Company Tax Return is the limited company's own return of its profits to HMRC. It's often called "the CT600", but the CT600 form is only one part — a complete return is the CT600 plus the company's accounts plus the Corporation Tax computations. An incomplete return can be treated as not delivered.

It runs on the company's accounting period, not the tax year. The return is due 12 months after the accounting period ends — but the Corporation Tax itself is due earlier, 9 months and 1 day after the period ends. Paying before you file trips up a lot of first-time directors. The company tax return page covers it properly, including why a company's first year can need two CT600s.

The two returns side by side

Do directors have to file both?

This is the confusion this page exists for, and it runs in both directions.

"My company filed its CT600 — does that cover me?" No. The company's return covers the company's profits. Anything you personally take out — dividends especially — is your income, and if it isn't fully taxed through PAYE you may need your own Self Assessment return.

"I file Self Assessment — does that cover my company?" Also no. The company is a separate legal entity and files its own CT600 every year regardless of what you file personally.

"So do all directors file Self Assessment?" No — and this one is a stubborn myth. Being a director is not, by itself, on HMRC's list of reasons to file. What puts a director into Self Assessment is the ordinary criteria: untaxed income such as dividends, Capital Gains Tax to pay, the High Income Child Benefit Charge, or simply HMRC sending a notice to file. Plenty of directors who take only a PAYE salary never need a personal return. If you're unsure, check rather than assume in either direction.

Which return do you need?

• Sole trader: Self Assessment only. There is no CT600 in your life — see sole trader accounts.
• Limited company: the company files a CT600 every year, and you personally may also need Self Assessment, per the criteria above.
• Not sure whether you're a company at all? Two minutes on the register settles it — sole trader or limited company.

Frequently asked questions

Is Self Assessment the same as Corporation Tax? No. Self Assessment collects income tax from individuals. Corporation Tax is what a limited company pays on its profits, reported on the Company Tax Return. Different taxes, different returns, different deadlines.

My company made a loss. Does it still file a Company Tax Return? Yes. A company served a notice to file must file, profit or loss — the return is how the loss goes on record (which matters, because losses can reduce future tax bills).

Do I need to file Self Assessment just because I'm a director? No. Being a director isn't on HMRC's list by itself. You file if you meet a normal criterion — untaxed dividend income, Capital Gains Tax, the High Income Child Benefit Charge — or if HMRC sends you a notice.

Can I do both returns in one place? They're filed separately: Self Assessment through your personal HMRC account or software, the Company Tax Return through commercial software. The free joint filing service that once combined company filings closed on 31 March 2026 — see what changed.

Why is my company's tax due before its return? That's how the deadlines are set: Corporation Tax is payable 9 months and 1 day after the period ends, while the return itself isn't due for 12 months. Work out the tax early enough to pay on time, even though the filing deadline is later.

Two returns, two deadlines, one person keeping track of it all? See how we handle both →