What closed, and what didn’t

HMRC closed its own online service for filing accounts and Company Tax Returns on 31 March 20261. Three things have not changed:

  • You still file. A company that gets a notice to deliver a Company Tax Return must file one, even with a loss or no tax to pay4.
  • The deadline is the same. 12 months after the end of the accounting period, with the tax itself due earlier4.
  • Companies House is separate. You still file your annual accounts with Companies House, online or on paper by post1. That changes in April 2028, when Companies House will only accept accounts through commercial software, though its web filing will stay open for confirmation statements and other changes5.

What a Company Tax Return is made of

A Company Tax Return is the CT600 form, any supplementary pages, and the company’s accounts and tax computations2. HMRC requires the computations and accounts in Inline XBRL (iXBRL), a tagged format that software produces for you2. HMRC tells former users of its service to choose software that can file each element they need: the CT600, the Corporation Tax computation, and the company’s accounts1.

You needGoes toNotes
CT600, plus supplementary pages (such as CT600A for loans to directors)HMRCOnly through commercial software, unless you have a reasonable excuse or file in Welsh1
Tax computation, in iXBRLHMRC, with the CT600Part of the return2
Accounts, in iXBRLHMRC, with the CT600Part of the return2
AccountsCompanies HouseOnline or by post until April 2028; then software only6,5

Your options now

  • An accountant, who prepares and files the return as your agent.
  • Software that you fill in yourself, where you enter the figures from your own accounts.
  • Software that prepares the return for you from your bank transactions or bookkeeping, for you to check before it is filed.

Whichever you choose, the directors stay responsible for the company’s accounts and return, even when someone else does the work8.

What to check in CT600 software

  1. It is on HMRC’s list. HMRC publishes the commercial software it accepts returns from, and says it accepts returns filed using any product on that list3.
  2. It covers every part you need: the CT600, the computation and the accounts, in iXBRL1,2.
  3. It files your accounts with Companies House too, or you are happy to do that separately. Some listed software files the return and the annual accounts together3.
  4. It handles your situation: a first period longer than 12 months (two returns), a director’s loan (CT600A), losses, a dormant year, or the simpler accounts a micro-entity can file.
  5. The price you’ll pay is shown in full, including anything charged per return or per year.

Dormant companies

A dormant company does not need software for a CT600 unless HMRC has sent it a notice to deliver one. Once you’ve told HMRC the company is dormant, you don’t file another return unless you get a further notice7. You must still file accounts and a confirmation statement with Companies House every year7,1. The dormant companies guide explains what counts as dormant.

Changing or re-filing an earlier return

To amend a return you already sent, or re-file one that was rejected, you can use commercial software, write to or send a paper return to the Corporation Tax office, or use an agent1. Changes are usually due within 12 months of the filing deadline4. To correct accounts already filed at Companies House, use software or send paper accounts by post1.

Bringing last year’s figures across

Your accounts show last year’s figures alongside this year’s. Your last filed accounts are public on the Companies House register, so a new tool can read the previous year’s balance sheet from there rather than you retyping it. Keep a copy of your last CT600 and computation too, for losses carried forward and any director’s loan.

Your first CT600 without CATO: a checklist

  1. Find your accounting period and deadlines. The CT600 is due 12 months after the period ends, and the tax 9 months and 1 day after4. The When are company accounts due? guide has worked examples.
  2. Find your company’s UTR and its HMRC business tax account login.
  3. Have your bank statements for the whole period, and last year’s accounts.
  4. Check for a director’s loan still owed at the year end: it can mean extra tax on the CT600A. See director’s loan accounts and s455.
  5. Work out your Corporation Tax. The Corporation Tax calculator gives the figure with marginal relief.
  6. Choose your software, prepare the accounts and computation, check them, and file the CT600 to HMRC and the accounts to Companies House.

Fileyear prepares the accounts, the tax computation and the CT600 from your bank statement, for you to check before anything is filed, and files the accounts to Companies House and the return to HMRC in the same sitting.