Company accounts and tax, explained plainly.
What’s changing at HMRC and Companies House, and what it means for your filings. Filing a Company Tax Return? Start with the CT600 guides.
HMRC’s free Company Tax Return service has closed: what to do now
HMRC’s free online service for filing company accounts and Company Tax Returns closed on 31 March 2026. Here’s how to file your CT600 now, and what changes for your Companies House accounts.
Companies House accounts: software-only filing from April 2028
From April 2028, every company must file its accounts with Companies House through software, in iXBRL. What changes, who it affects, and how to get ready.
What is iXBRL, and does your company need it?
iXBRL is the tagged format HMRC requires for company accounts and tax computations, and Companies House will require for all accounts from April 2028. A plain explanation.
How to file a CT600 (Company Tax Return)
How to file your company’s CT600 online: who must file, what the return includes, what you need, the deadlines, and how to correct a return after filing.
Filing your company accounts with Companies House
Which accounts a private company files with Companies House, what goes in them, the 9-month deadline, the authentication code and late filing penalties.
Corporation Tax deadlines: filing, paying and penalties
When Corporation Tax is due: pay 9 months and 1 day after your accounting period ends, file your CT600 within 12 months. Dates, examples and penalties.
Dormant company accounts: what to file
A dormant company still files accounts and a confirmation statement with Companies House. What dormant means, and when HMRC wants a CT600.
What is a CT600?
A CT600 is the form at the centre of a Company Tax Return. Here’s what it is, who has to send one, what’s on it, when it’s due and how it’s filed.
What needs to go with a CT600?
A CT600 doesn’t go to HMRC on its own. Here’s what has to accompany it: the company’s accounts, a tax computation in iXBRL and any supplementary pages.
Accounting periods for Corporation Tax explained
A Corporation Tax accounting period can’t be longer than 12 months, so it isn’t always the same as the period of your accounts. Here’s when the two differ and how many returns you file.
CT600 supplementary pages explained
The CT600 has supplementary pages for particular situations, from CT600A for loans to directors to CT600P for creative industries. Here’s what each is for and which small companies need.
CT600A explained: loans to directors and shareholders
CT600A is the supplementary page for a close company’s loans to its participators. Here’s who completes it, the section 455 tax rates, how relief works when a loan is repaid, and the 2026 rate change.
How to amend a CT600 after filing
You can usually amend a Company Tax Return within 12 months of the filing deadline. Here’s how to do it, what HMRC can correct itself, and what to do once the deadline has passed.
CT600 software: what to look for
Now that HMRC’s free filing service has closed, every Company Tax Return needs commercial software. Here’s what to check before you choose, and which kind of product suits which company.
CT600L explained: the R&D supplementary page
CT600L is the supplementary page for research and development claims on a Company Tax Return. Here’s who completes it, the two forms HMRC needs first, and how it feeds the CT600.
Micro-entity accounts and Corporation Tax
Micro-entities can file very short accounts at Companies House, but their Company Tax Return is the same as any other company’s. Here’s what a micro-entity sends to HMRC, and when.
What goes in a Corporation Tax computation?
A Corporation Tax computation takes the profit in your company’s accounts and works out the taxable profit and the tax. Here’s what goes in one, with a worked example.