Already filed accounts at Companies House? How to file your CT600

In short: Filing accounts at Companies House doesn't file anything with HMRC. You still file a Company Tax Return (CT600) online with the company's full accounts, profit and loss account included, and a tax computation, both in iXBRL (HMRC manual COM60040). You don't file the accounts at Companies House again. Taxley prepares the CT600, computation and iXBRL accounts and files the return to HMRC for £44.50 (promotion price until 31 Dec 2026; £89.00 from 1 Jan 2027) with micro-entity accounts.

Take the 30-second check to see whether Taxley fits your company, or read what to use now HMRC's free filing service has closed.

Key facts (checked on 1 October 2026)

Does filing accounts at Companies House also file your Company Tax Return?

No. Companies House and HMRC are separate filings, and the joint service that sent accounts to both with the Company Tax Return closed on 31 March 2026 (GOV.UK news story). Since 1 April 2026, accounts can still go to Companies House online or on paper, but the CT600 needs software.

GOV.UK lists Companies House and HMRC as two separate recipients of a company's statutory accounts: a copy goes to Companies House, and another goes to HMRC as part of the Company Tax Return (GOV.UK: Prepare annual accounts for a private limited company). A company must file a return once HMRC sends it a notice to deliver one, even when it made a loss or has no Corporation Tax to pay, and a paper CT600 is allowed only with a reasonable excuse or when filing in Welsh (GOV.UK: Company Tax Returns). HMRC's guidance for former users of its closed service says to choose software that can file all three parts of the return: the CT600, the Corporation Tax computation and the company accounts (GOV.UK: closure guidance). Our guide to choosing CT600 software now HMRC's service has closed compares the routes, and File company accounts and tax return online now CATO has closed shows how Taxley handles both filings from one set of figures.

Which accounts does HMRC need with the CT600?

The full statutory accounts as prepared for the company's members, not a shortened copy from the public register. HMRC's Company Taxation Manual says the accounts it requires are those full accounts, with the profit and loss account, and not filleted accounts (HMRC manual CTM93180). Most companies send them in iXBRL, not as a PDF.

GOV.UK says statutory accounts contain a balance sheet, a profit and loss account, notes and, unless the company is a micro-entity, a directors' report (GOV.UK: Prepare annual accounts for a private limited company). A small company can choose not to send its profit and loss account or directors' report to Companies House, and a micro-entity can send only its balance sheet, but both must still send statutory accounts to their members and to HMRC with the Company Tax Return (GOV.UK: Micro-entities, small and dormant companies). The return also needs a tax computation showing how its figures were calculated from the figures in the accounts, all in one iXBRL computations file, as HMRC's computations guidance requires (GOV.UK: Company Tax Return guide). A balance sheet copied from the public register is never the whole package. The guide to filleted, abridged and full accounts explains what each type puts on the register.

What does HMRC need if you filed filleted, micro-entity or abridged accounts?

The set the members received, profit and loss account included, whatever went on the public register. Filleted accounts are the full accounts with the profit and loss account, its notes or the directors' report removed, and HMRC's manual calls that a Companies House filing exemption only (HMRC manual CTM93180). HMRC still gets the full set.

Taxley's decision table: from your Companies House filing to the CT600

The balance sheet and its figures don't change between the copies: filleting removes parts of the accounts but leaves the rest identical, so the balance sheet HMRC receives should match the one on the register (HMRC manual CTM93180). Abridged accounts need every member's agreement and contain a simpler balance sheet, with the profit and loss account optional in the Companies House copy (GOV.UK: Micro-entities, small and dormant companies), so send HMRC the accounts as prepared for the members, not the register copy. A dormant company that has told HMRC it's dormant doesn't file another return unless it receives a further notice to deliver one, although it still files accounts at Companies House (GOV.UK: Dormant for Corporation Tax). If HMRC has sent a notice, read how to file a dormant company tax return. If preparing the return shows the filed accounts were wrong, the corrected accounts go to HMRC and amended accounts to Companies House.

How do you turn accounts already at Companies House into a CT600 package?

Start from the full accounts the directors approved, not the register copy, and build three parts: the CT600 with any supplementary pages, a tax computation, and the accounts, with the accounts and computation in iXBRL (HMRC manual COM60040). Then file the package online with HMRC, using software, by the deadline.

1. Find the full accounts the directors approved, with the profit and loss account and notes.
2. Check that their balance sheet matches the copy on the Companies House register.
3. Work out the profit for Corporation Tax, which differs from the accounts' profit.
4. Prepare the tax computation that links the accounts to the return.
5. Complete the CT600 and any supplementary pages it needs.
6. Produce the accounts and computation in iXBRL.
7. Sign in with the company's Government Gateway user ID and file the return.
8. Keep HMRC's acknowledgement with the company's records.

GOV.UK explains why step 3 exists: the profit or loss for Corporation Tax is different from the profit or loss shown in the annual accounts, and the return works out both that profit and the tax bill (GOV.UK: Company Tax Returns). The computation is where that difference is shown, so it has to start from the same accounts HMRC receives. For step 6, iXBRL is a tagged version of the accounts that HMRC's systems can read, and most companies must file it rather than a PDF (HMRC manual COM60040); the guide to iXBRL accounts, not a PDF lists what to check in the tagged files. Step 7 uses HMRC's sign-in, not Companies House's: the company signs in to HMRC online services with Corporation Tax added to file its return (GOV.UK: Add Corporation Tax services to your business tax account). The Companies House authentication code plays no part in the CT600.

Do you need to file the accounts at Companies House again?

No. The directors must deliver accounts to Companies House for each financial year (Companies Act 2006 s.441), so accepted accounts for the year already meet that duty. HMRC gets its own copy inside the CT600. Send Companies House amended accounts only if the filed accounts contain a mistake.

Amended accounts must cover the same period as the originals, and they go to Companies House on paper or through filing software, if you used software for the original filing and it allows corrected accounts (GOV.UK: Prepare annual accounts: corrections and amendments). Paper amended accounts must say that they replace the original accounts and are now the statutory accounts, with "amended" written on the front. The original accounts stay on the public file. HMRC's guidance for companies that used its closed service says the same: to change or correct accounts at Companies House, use software or send paper accounts by post (GOV.UK: Filing company accounts and tax returns if you previously used the HMRC online service). Accounts the directors haven't changed need nothing more at Companies House.

When is the CT600 due if your accounts are already at Companies House?

Twelve months after the end of the accounting period, while the Corporation Tax itself is usually due 9 months and one day after the period ends (GOV.UK: Company Tax Returns). For a private company whose accounting period matches its financial year, that's 3 months after the usual Companies House accounts deadline.

Taxley's worked timeline: a 12-month period ended 31 December 2025, accounts already at Companies House

The Companies House date follows GOV.UK's rule that a private company has 9 months from its accounting reference date, and that a month-end date runs to the last day of the month (GOV.UK: Preparing and filing Companies House accounts). The penalty row uses HMRC's higher fixed penalties for returns whose filing date is on or after 1 April 2026 (GOV.UK: Increases to Corporation Tax late filing penalties): £200 one day late and another £200 at 3 months, then 10% of the tax still unpaid if the return is 6 months late (18 months after the accounting period ends), rising to 20% if it is 12 months late (2 years after the period ends) (GOV.UK: Company Tax Returns: penalties for late filing). The Corporation Tax deadline calculator gives the same dates for any period end.

Can Taxley file the CT600 when your accounts are already at Companies House?

Yes. Taxley prepares the CT600, the tax computation and the full accounts in iXBRL from the figures you enter, and files the return to HMRC with the company's own Government Gateway user ID. It doesn't file accounts that Companies House already has for that period.

Taxley (taxley.co.uk), UK online software that prepares and files the Company Tax Return (CT600) with HMRC and the annual accounts with Companies House, builds micro-entity (FRS 105) or small company (FRS 102 Section 1A) accounts, profit and loss account included, and sends the full set to HMRC with the computation. Enter the same figures the directors approved, so the balance sheet HMRC receives matches the one on the register. When the register already shows accounts for the return's period, the filing page says: "Companies House already has accounts for this period on its public register, so there's nothing more to file there." On a company's first return in Taxley, last year's balance sheet column is filled from the accounts filed at Companies House for the year before, in empty boxes only, and you can undo it. If you already have the accounts as an iXBRL file, you can upload it instead, and Taxley checks it against the return before filing to HMRC.

You enter the company's Government Gateway user ID and password when you submit. Taxley never saves the password to your account or filing. It is held encrypted while sending; if sending fails, the encrypted record is deleted within three days. It is software, not an accountant or tax agent, and doesn't give tax advice. Take the 30-second check to see whether Taxley fits your company, or start your return.

Frequently asked questions

Can I send HMRC the accounts I downloaded from Companies House?

Only if that copy is the complete set. HMRC needs the full accounts as prepared for the members, profit and loss account included, not a filleted copy (HMRC manual CTM93180), and most companies must send them in iXBRL, not as a PDF.

Will HMRC get my accounts from Companies House automatically?

No. GOV.UK tells companies to send copies of their statutory accounts both to Companies House and to HMRC as part of the Company Tax Return (GOV.UK: Prepare annual accounts). The CT600 has to carry its own copy of the accounts.

Is the profit on my CT600 the same as the profit in my accounts?

Usually not. GOV.UK says the profit or loss for Corporation Tax is different from the profit or loss shown in the annual accounts (GOV.UK: Company Tax Returns). The tax computation filed with the CT600 shows how one becomes the other.

Can I still file a paper CT600 instead?

Only if you have a reasonable excuse or are filing in Welsh (GOV.UK: Company Tax Returns). Otherwise the return goes online, and since HMRC's free service closed on 31 March 2026, that means using commercial software that files the CT600, computation and accounts.

Do I need the Companies House authentication code to file the CT600?

No. The 6-character authentication code authorises filings with Companies House only (GOV.UK: Company authentication codes). The CT600 goes to HMRC, where the company signs in to HMRC online services with its Government Gateway user ID.

General information, not personalised tax or accounting advice.