HMRC's free CT600 service has closed. Here's how to file now.
HMRC and Companies House's joint online service for company accounts and tax returns closed on 31 March 2026. Since 1 April 2026, a company files its Company Tax Return (CT600) with commercial software. Clients Assistant is that software: prepare the return free, then file it from £5 + VAT a year.
Companies House filing opens soon. You can file the CT600 with HMRC from Clients Assistant now. Until Companies House filing opens here, file the accounts with Companies House yourself, online or by post.
Start for freeWhat changed on 1 April 2026
The free service let small companies with simple affairs file their accounts and tax return in one place. HMRC closed it because it no longer met modern digital standards or recent changes to company law. Here is where each part goes now.
| Until 31 March 2026 | From 1 April 2026 | |
|---|---|---|
| Company Tax Return (CT600) | HMRC's free online service | Commercial software, filed online |
| Tax computation | Built in HMRC's service | Prepared in your software and sent with the return |
| Accounts for HMRC | Built in HMRC's service | Sent with the return from your software |
| Accounts for Companies House | The joint service, or Companies House | Companies House, online or by post |
A paper return is only accepted if you have a reasonable excuse or you're filing in Welsh.
What you need to file now
HMRC's advice is to choose software that files the CT600, the Corporation Tax computation and the company's accounts. To file, you'll also need:
- The company's 10-digit Corporation Tax UTR
- The Government Gateway user ID and password for the company's HMRC online services account, with Corporation Tax added, or your accountant's agent sign-in
- The year's figures: from your books, a trial balance from Xero, QuickBooks or Sage, or a spreadsheet
Moving to Clients Assistant
Find your company
Enter the company number. Its name, address and deadlines come from Companies House, and last year's figures can be read from the accounts on the register.
Bring in the figures
Use your Clients Assistant ledger, upload a trial balance from Xero, QuickBooks or Sage, fill in our Excel template, or type the figures in. Check the computation, accounts and CT600.
File and follow it through
Send the CT600 to HMRC with the company's Government Gateway sign-in or your agent's. HMRC's reply is collected for you and kept in the submission history.
Which companies it suits
Clients Assistant prepares micro-entity, small and dormant company accounts with the CT600, so it fits the companies that used HMRC's free service. It also handles what that service couldn't:
- Marginal relief for profits between £50,000 and £250,000, shared between associated companies
- A period of account of up to 18 months, split into two returns for you
- Directors' loans on the CT600A
- Charities' CT600E pages, and the CIC34 report for community interest companies
- Amending a return you've already filed
If your company has to prepare medium or large company accounts, Clients Assistant isn't the right tool.
What it costs
| Plan | Price | What it covers |
|---|---|---|
| Prepare | Free | Company details and deadlines from Companies House, the tax computation, accounts and CT600 previews, checks against HMRC's rules, deadline reminders |
| One dormant company | £5 + VAT a year | Filing the year's return and accounts for a dormant company |
| One company | £15 + VAT a year | Filing the year's return and accounts for any other company, including charities and CICs |
| Several companies | from £35 + VAT a year | For groups and accountants: bands from 3 to 1,000 companies |
All prices exclude VAT; 20% VAT is added at checkout, so £5 a year is £6.00 including VAT.
Questions people ask
On 31 March 2026. It was HMRC and Companies House's joint online service for filing company accounts and Company Tax Returns. Since 1 April 2026, companies file their CT600 with commercial software such as Clients Assistant.
Only if you have a reasonable excuse or you're filing in Welsh. Otherwise the return has to be filed online, which now means using commercial software.
Yes. Annual accounts still go to Companies House every year, online or by post. Clients Assistant prepares them from the same figures as your CT600.
Preparing the return is free. Filing is £5 + VAT a year for a dormant company and £15 + VAT a year for any other company. Accountants and groups can cover from 3 to 1,000 companies from £35 + VAT a year.
No. If your company's affairs are simple you can prepare and file the return yourself: Clients Assistant works out the tax, including marginal relief, and checks the return against HMRC's rules before you send it. If you have an accountant, they can file it for you with their HMRC agent sign-in.
Yes. Export the trial balance at the company's year end and upload it as it is, in Excel or CSV. Clients Assistant sorts each account into turnover, expenses, assets, liabilities or capital, and you check every line before the return is created.
The company's 10-digit Corporation Tax UTR, and the Government Gateway user ID and password for its HMRC online services account, with Corporation Tax added. An accountant can use their HMRC agent sign-in instead, once you've authorised them for Corporation Tax.
Yes. For a dormant company, Clients Assistant checks the company's Companies House record and books, then prepares dormant accounts. Charities can file the CT600 with the CT600E pages, and community interest companies get their accounts and CIC34 report prepared together.
Checked against GOV.UK on 15 October 2026. Sources: Closure of the service to file your company accounts and tax return.
Related guides and products
Dormant companies
What a dormant company still has to file, and when HMRC needs a CT600.
Dormant company returns →Corporation Tax
Everything Clients Assistant does for company tax returns and accounts.
Clients Assistant Corporation Tax →