ArticleBy Matvei Kostiuchenko
Do I need an accountant to file a CT600?
No law requires one. Whether you should use one depends on eight questions about your company, not on how confident you feel. Here is the test.
No. There is no legal requirement to use an accountant for a Company Tax Return. HMRC's own guidance says you can either get an accountant to prepare and file it or do it yourself. The real question is whether your company is simple enough that doing it yourself is sensible — and that has a fairly short answer.
What an accountant actually does for a small company
For a one-director company, the annual job is usually four things:
- Turn your records into statutory accounts — a profit and loss account and a balance sheet in the format the law requires.
- Work out taxable profit, which is not the same as the profit in the accounts: some costs are not allowable, equipment is handled through capital allowances, losses may be carried forward.
- Prepare and file the CT600 with the computation and the accounts attached in iXBRL.
- Apply judgement on the grey areas: is that laptop an expense or an asset, was that trip business, does the money you moved in create a director's loan.
Software can do the first three for a simple company. It cannot do the fourth. So the test is: how much of number four does your company have?
The eight-question test
Answer yes or no. If every answer is yes, filing yourself is reasonable. Two or more no's — get an accountant, at least for this year.
| # | Question |
|---|---|
| 1 | Does the company do one kind of business, in the UK only? |
| 2 | Is it a standalone company — no parent, no subsidiaries, no group? |
| 3 | Is all income from trading (invoices for work or sales), with at most a little bank interest? |
| 4 | Are you the only person paid — salary, dividends or both — with no other employees? |
| 5 | Can you list every cost of the year from your bank statement, and say what each one was for? |
| 6 | Did you buy nothing unusual — no property, no vehicle, no shares in other companies? |
| 7 | Are you not claiming R&D relief, creative-industry relief or anything else that needs a specialist? |
| 8 | Is this a normal 12-month year — not your first period, not a period after you changed the year end? |
Question 8 matters more than it looks. A first accounting period longer than 12 months has to be split into two returns, and that is where most first-time filers go wrong. It is still doable yourself — it just is not the year to be casual.
Where doing it yourself goes wrong
From the questions UK directors ask on forums, the mistakes cluster in five places:
- Equipment treated as an ordinary expense when it should go through capital allowances (the answer is usually the same tax, but the return has to show it correctly).
- Money you put in or took out not recorded as a director's loan, which can trigger a separate tax charge.
- Costs paid from your personal card never making it into the company's books.
- A loss year filed as "nothing to do" — you still file, and the loss carried forward saves tax later.
- Paying and filing confused. Corporation Tax is usually due nine months and one day after the year end; the return is due at twelve months. Directors regularly discover the first deadline after it has passed.
None of these needs an accountant to avoid. They need a process that asks the question before you press file.
What "no accountant needed" does not mean
It does not mean nobody looks at your numbers. A good filing tool runs the same checks an accountant would run first — does the balance sheet balance, does the computation match the accounts, are the boxes HMRC validates filled in — and refuses to send a return that would be rejected. It does not mean tax advice: if your company has a genuinely uncertain position, that is a professional's job, and the honest tools say so.
Which companies filefast will turn away
filefast is built for the company that answers yes to all eight. It checks this before you enter a single figure.
Not for filefast — go to an accountant:
- Charities. They file a different return, the CT600E.
- Companies in liquidation, or not active at Companies House. A liquidator runs the company's affairs.
- Close investment-holding companies — a company that only holds investments. Different tax rates apply.
Not yet — filefast tells you at the start and you'll need an accountant for this year:
- Part of a group (a parent or subsidiaries)
- Claiming R&D relief
- Rental income
- Income from outside the UK
- Sold shares or property in the year
- More than one trade
- An accounting period that started before 1 April 2023
Everyone else — one trade, UK income, a standalone company, a normal year — adds the company from the Companies House register, enters the year's figures, and filefast produces the computation and accounts in iXBRL, runs HMRC's validation checks, and files the CT600 directly with HMRC.
filefast is in early access: the first 50 companies to have a CT600 accepted by HMRC through it keep filing for free, for life. How it works and the terms.
Sources: Company Tax Returns: overview and Accounting periods for Corporation Tax on GOV.UK. Rules as at 26 September 2026; last reviewed 26 September 2026.
Matvei Kostiuchenko, founder of filefast. Not an accountant. This article is general information, not a substitute for regulated tax advice.