Trading company filing
What's included
- CT600 return
- iXBRL tax computation & accounts
- Companies House accounts for eligible companies
- HMRC & Companies House status tracking
Filing Guide
File your CT600 online.
This page is a step-by-step guide to preparing and filing a CT600 Corporation Tax return online with WeFile. It helps you prepare the required details, understand the process and avoid common submission problems.
Related: CT600 Software · Dormant Accounts · Tax Calculator · Compare CT600 Software · Amending a CT600
THE BASICS
Filing a CT600 online in 2026
A CT600 is the Company Tax Return. HMRC's free CT600 filing service (CATO) closed on 31 March 2026, so companies now file online using commercial software. WeFile appears on HMRC's Corporation Tax commercial software suppliers list. Learn more about the closure of HMRC's free filing service.
CHECKLIST
What you need before you start
Gather these details before filing. New to the Company Tax Return?
Read the CT600 guide.
Company UTR
Your 10-digit Unique Taxpayer Reference, found on correspondence from HMRC.
Government Gateway
Your User ID and password, fully enrolled for Corporation Tax services.
Companies House Auth Code
The 6-alphanumeric code for your company if you are filing accounts simultaneously.
Accounting Period Dates
Confirm your start and end dates. A Corporation Tax accounting period cannot exceed 12 months.
Trial Balance
Finalised bookkeeping figures to input your Profit & Loss and Balance Sheet accurately.
SUBMISSION PACKAGE
What HMRC receives in an online CT600 submission
WeFile generates the iXBRL tax computation and accounts from your figures. Learn more about iXBRL accounts software.
CT600 form
The Company Tax Return, prepared as CT600 Version 3.
Tax computation
The iXBRL-tagged calculation supporting the tax figures in the return.
Statutory accounts
The iXBRL-tagged accounts submitted with the return.
Supplementary pages supported: CT600A (loans to participators / s455) and CT600E (charities and CASCs). Other supplementary pages (CT600B–D and CT600F–P) are not supported; check what your company needs before you start.
WALKTHROUGH
The WeFile wizard
Our guided workflow simplifies preparation and submission.
Select Company & Period
We pull your expected accounting periods from Companies House data to help your dates align. Check the period against HMRC's records.
Enter Profit & Loss
Input your revenue, costs, and expenses. We'll automatically identify your net trading profit.
Balance Sheet & Capital Allowances
Detail your assets and liabilities, and apply capital allowances to the relevant asset pools.
Review Computed Tax
Review our automated tax computation, including Marginal Relief where applicable.
Provide Credentials
Securely input your Gateway ID and authentication codes just before submission.
Pay & Submit
Complete the transaction to dispatch the return to HMRC and, where applicable, submit accounts separately to Companies House. Check each authority's response.
FILING OPTIONS
HMRC portal vs commercial software
CATO was HMRC's former free filing service. Government Gateway remains the sign-in you use for Corporation Tax; it is not a separate filing-software option.
| Feature | Former HMRC CATO service | WeFile commercial software |
|---|---|---|
| Availability | Closed 31 March 2026 | Available |
| iXBRL accounts & computation | Generated limited simple-company accounts | Generated from your figures |
| Companies House accounts | Separate filing | Same workflow for eligible companies |
| Supplementary pages | Former service closed | CT600A and CT600E |
| Cost | Was free | Per-filing fee |
What it costs to file online with WeFile
Simple per-filing pricing for trading and dormant companies.
WeFile's price only, not a market benchmark
Dormant company filing
What's included
- CT600 return where required
- iXBRL tax computation & accounts
- Companies House accounts for eligible companies
- HMRC & Companies House status tracking
DEADLINES & AFTER FILING
Key dates, receipts and penalties
9 months + 1 day
Corporation Tax payment
Normally due 9 months and 1 day after the accounting period ends for companies outside the instalment-payment regime.
9 months
Companies House accounts
Normally due 9 months after the accounting reference date for a private company, or 21 months after incorporation for its first accounts.
12 months
CT600 return
Normally due 12 months after the Corporation Tax accounting period ends.
What happens after you submit
- Step 1
Gateway response & IRmark receipt
Following a successful gateway response, you receive an IRmark receipt — HMRC's electronic proof of receipt. This does not guarantee the return has passed later back-office checks.
- Step 2
Status tracking
WeFile tracks HMRC and Companies House responses separately, because each authority accepts or rejects its filing independently.
- See each authority's latest status on your filing page.
- We check HMRC and Companies House for responses automatically.
- We email you when the filing is accepted, or if it is rejected.
- Step 3
Download & follow up
Once available, you can download your CT600 and generated accounts from your dashboard. Check each authority's status and follow up on any rejection.
Late filing penalties
For returns with a filing date on or after 1 April 2026
- 1 day late
- £200
- 3 months late
- £400
- Third successive late return
- £1,000 / £2,000
- 6 and 12 months
- Tax-geared
Penalties may apply
BEFORE YOU SUBMIT
Tips for a smooth submission
- Reconcile your profit and loss and balance sheet before starting; WeFile requires them to reconcile.
- Confirm HMRC's accounting period dates and split periods longer than 12 months into separate returns.
- Check that the UTR matches the company number.
- Keep the IRmark receipt and check the filing status afterwards.
- File an amendment for the same period rather than another original return.
Read about CT600 submission errors and check the treatment of allowable and disallowable expenses before submitting.
TROUBLESHOOTING
Common reasons a CT600 is rejected
Check these common pitfalls before submitting. For receipt, back-office checks and what to do after a rejection, read the CT600 submission to HMRC guide. No check guarantees acceptance.
UTR / Company Number Mismatch
HMRC cross-references your Company Registration Number with the UTR you provide. Check both identifiers before resubmitting.
Missing Original Return
If you submit an amendment but HMRC has no record of an original return for that period, it may be rejected.
Authentication Failures
Incorrect Government Gateway credentials, or an account not enrolled for Corporation Tax, can prevent filing.
Unrecognised Periods
HMRC's accounting periods can differ from Companies House dates; check HMRC's records.
FAQ
Frequently asked questions
Yes. Directors can file their company's Corporation Tax returns online. Commercial software such as WeFile helps prepare the calculations and formatting required for supported filings.
The electronic gateway usually responds within seconds to minutes, but its receipt is not a guarantee that HMRC's later back-office checks have posted the return to the company's record. Check subsequent notices and your filing status.
When you first register for Corporation Tax online, HMRC sends an activation code by post. Activate your account before attempting to file with those credentials.
Yes, you can file an overdue return, but HMRC may charge late-filing penalties and interest may apply to late tax payments.
A single Corporation Tax accounting period cannot exceed 12 months. If your accounts span a longer period, you may need two separate CT600 returns.
HMRC generally expects statutory accounts with the CT600. Companies House accounts are a separate filing with their own deadline and acknowledgement; WeFile supports both submissions for eligible companies.
No. HMRC's free CT600 filing service, CATO, closed on 31 March 2026. Companies filing online now use commercial software.
Yes. HMRC generally requires the accounts and tax computation in iXBRL for online Corporation Tax returns, with limited exceptions. WeFile generates both from the figures you enter.
Yes, if HMRC has issued a notice to file a Company Tax Return for the dormant company. Check the company's position with HMRC before filing.
For returns with a filing date on or after 1 April 2026, HMRC's fixed penalties are £200 at one day late and £400 at three months late. For a third successive late return, these rise to £1,000 and £2,000 respectively. Further tax-geared penalties may apply at six and twelve months.