CT600 FILING GUIDE
Online Corporation Tax filing: a step-by-step guide for UK limited companies
Since HMRC’s free joint filing service closed on 31 March 2026, online CT600 filing is via commercial software or an agent. This guide helps you organise the information, checks and separate submissions involved.
Creating an account is free. You pay the filing fee per filing.
01 / KNOW THE OBLIGATIONS
What online Corporation Tax filing involves
For a supported company, the HMRC package includes a CT600 Version 3 return, applicable supplementary pages, statutory accounts and a tax computation in the required electronic format, including iXBRL where applicable. Companies House accounts are a separate filing, even when prepared in the same workflow.
You authorise the HMRC submission using your own Corporation Tax-enrolled Government Gateway credentials. For a fuller explanation of the return, read our Company Tax Return guide. The guide to HMRC’s free joint service closure explains what changed on 31 March 2026.
02 / A WORKABLE ORDER
5-step CT600 filing checklist
Work through the tasks in order, tick what you have prepared and download a copy for your records. Your selections stay in this browser.
Confirm your accounting period and deadlines
Check the dates for the tax return, tax payment and separate accounts filing.
Gather company details and access codes
Have the identifiers and credentials needed for each applicable submission.
Prepare or import your P&L and balance sheet
Use your records to prepare the accounts figures and review comparatives.
Review tax adjustments and the computation
Check how the accounting figures become the Corporation Tax calculation.
Review, authorise and submit to HMRC and Companies House
Check the documents and track the result from each applicable destination.
Your ticks are stored only in this browser. Downloading the PDF does not send your selections to WeFile.
READY TO BEGIN?
Start your filing
Add your company and prepare your figures before paying the applicable per-filing fee.
Confirm the payable price before purchase; displayed prices may use a fallback if current pricing is unavailable.
03 / THREE DIFFERENT DATES
Online Corporation Tax filing deadlines
Payment, the CT600 and Companies House accounts have separate deadlines. Check the dates that apply to your company rather than relying on one date for all three.
| Obligation | Usual deadline | Check |
|---|---|---|
| Pay Corporation Tax | Usually nine months and one day after the tax period ends | Large companies may have to pay by instalments. |
| File the CT600 | Usually 12 months after the accounting period ends | An accounts period over 12 months normally needs two Corporation Tax returns. |
| File private-company accounts | Normally nine months after the accounting reference date | First accounts can have a different deadline; check the date for your company. |
HMRC late-filing penalties
For CT600 returns with a filing date on or after 1 April 2026, the following HMRC penalties can apply. Companies House late-accounts penalties are separate.
| Delay | Potential penalty |
|---|---|
| One day late | £200 fixed penalty |
| More than three months late | A further £200; £400 total in fixed penalties |
| Three successive late returns | £1,000, then a further £1,000 after three months |
| Six and 12 months late | An additional tax-geared penalty at each point, normally 10% of unpaid Corporation Tax |
Read the Corporation Tax deadlines and penalties guide for more detail.
04 / PREPARE YOUR RECORDS
Information you need before filing
The details you need depend on the company and its return. Gather your source records before entering figures; check any missing information with the relevant authority or an adviser.
Company
- Company number and Corporation Tax UTR
- Accounting period and accounting reference date (ARD)
- Companies House authentication code, if filing accounts there
Access
- Corporation Tax-enrolled Government Gateway user ID and password
Financials
- Profit and loss, balance sheet and supporting records
- Trial balance or bookkeeping export, if importing
- Prior-year figures for comparatives
Tax
- Capital allowance expenditure and relevant asset additions
- Losses brought forward
- Outstanding director loans and associated companies count
Payment
- Bank details if a repayment is due
05 / FROM FIGURES TO DOCUMENTS
How WeFile's wizard handles P&L and balance sheet calculations
Enter figures or import a trial balance from Xero, QuickBooks Online, FreeAgent or CSV. The profit and loss and balance sheet must reconcile: current-year profit flows into retained earnings, while capital and reserves comprise share capital, any share premium and capital redemption reserve, and closing retained earnings.
- 01Your figures
- 02Reconciliation checks
- 03Tax computation
- 04Accounts + CT600
- 05HMRC & Companies House
Corporation Tax is calculated from your inputs, including relevant Marginal Relief, associated companies, capital allowance pools, losses and the deductions allowance. For supported account types, WeFile generates FRS 105 micro-entity or FRS 102 Section 1A accounts with iXBRL tagging. Applicable close-company loans can be included on CT600A for the s455 calculation.
Reconciliation checks help reduce errors; they do not guarantee acceptance by HMRC or Companies House. You remain responsible for the information submitted.
06 / KNOW WHICH TOOL DOES WHAT
WeFile vs the manual HMRC route
HMRC’s online Corporation Tax account remains useful for managing and paying tax. It is not the former free joint CT600 filing service, which closed on 31 March 2026.
| Feature | HMRC online account | WeFile |
|---|---|---|
| CT600 submission form | Not available in the online account since the free joint filing service closed. | Prepare and submit supported CT600 Version 3 returns. |
| Accounts generation | Not an accounts preparation tool. | Generate supported FRS 105 or FRS 102 Section 1A accounts. |
| iXBRL | Not generated by the online account. | Generate supported tagged accounts and tax computations. |
| Automatic tax calculation | Not a CT600 calculation workflow. | Calculate from the figures and adjustments you enter. |
| Reconciliation checks | Not part of the online account’s CT management tools. | Check relationships between entered accounts figures. |
| Imports | Not a CT600 trial-balance import tool. | Import from Xero, QuickBooks Online, FreeAgent or CSV. |
| Companies House in the same workflow | Companies House accounts are filed separately. | Where eligible, prepare in one workflow and track a separate submission. |
| Price | Free account access; not a CT600 filing form. |
See the full comparison of HMRC account tasks and filing software.
07 / REVIEW WITH CARE
Common pitfalls when filing online without an accountant
Software can check relationships between figures, but it cannot establish whether your underlying records or tax treatment are correct. Review these points against your circumstances.
Period dates and ARD
The Corporation Tax accounting period may differ from the accounts period. An accounts period over 12 months normally requires two CT600 returns.
Disallowable expenses
Check whether costs such as business entertainment or fines must be added back when calculating taxable profit.
Capital allowances
Review qualifying additions and pool treatment. The Annual Investment Allowance does not apply to cars.
Associated companies
The number of associated companies affects the limits used for the small profits rate and Marginal Relief.
Director’s loans
An overdrawn loan account can require a CT600A and an s455 calculation; check the dates and any repayments.
Figures that do not reconcile
Check that profit flows into retained earnings and that assets equal liabilities plus capital and reserves.
Account-type eligibility
Do not assume micro-entity exemptions apply. Size tests have exclusions and a two-year qualification rule.
Credentials and two destinations
Check Government Gateway access and the Companies House authentication code. A successful HMRC return does not file the separate accounts.
For expense treatment, consult our allowable expenses guide. For access and rejection issues, see HMRC CT600 submission errors explained.
08 / CHOOSE THE RIGHT PRESENTATION
FRS 105 or FRS 102 Section 1A?
The accounts standard depends on eligibility, not just preference. The size tests have exclusions and a two-year qualification rule; thresholds alone do not establish that a company qualifies.
| Presentation | Standard and eligibility | Important distinction |
|---|---|---|
| Micro-entity | FRS 105. For financial years beginning on or after 6 April 2025, at least two of: turnover no more than £1 million, balance sheet no more than £500,000, and no more than 10 employees on average. | Fair value accounting is not permitted under FRS 105. |
| Small company | FRS 102 Section 1A, where the small-company regime applies. Check the applicable tests, exclusions and qualification rules. | Different presentation and disclosure requirements apply. |
Try the indicative FRS 105 eligibility checker, then read the micro-entity accounts guide or small-company accounts guide. Seek professional advice if the correct standard is unclear.
QUESTIONS, ANSWERED
Online Corporation Tax filing FAQs
Ready to prepare your filing?
Create an account, review your figures and pay the filing fee when you’re ready to submit.
This guide provides general information, not accounting, legal or tax advice. Check the rules for your circumstances and seek professional advice where needed. WeFile is independent of HMRC and Companies House. WeFile appears on HMRC's Corporation Tax commercial software suppliers list; inclusion does not imply endorsement, accreditation or guaranteed acceptance.