Online CT600 software for UK small businesses.
Prepare and submit your Company Tax Return to HMRC and, for supported account types, your statutory accounts to Companies House — with the profit and loss, balance sheet, corporation tax and iXBRL tagging worked out automatically.
What is CT600 software?
A CT600 is the Company Tax Return submitted to HMRC by companies within the charge to Corporation Tax. Since HMRC's free Company Tax Returns online service closed on 31 March 2026, most companies must file using commercial software, or through an agent using such software; paper returns are permitted only in narrow circumstances HMRC sets out. CT600 software prepares, validates and transmits that return electronically.
The Company Tax Return guide explains the wider filing obligation. In practice, CT600 software brings together eight distinct jobs:
Prepare the CT600 form
The form reports the company's tax position in the relevant CT600 Version 3 boxes. Software identifies the accounting period, collects the figures and declarations needed for that return, and places them in the appropriate fields. A Corporation Tax accounting period cannot exceed 12 months, so a longer period of accounts may require two returns. A company must still respond when HMRC has issued a notice to deliver a return, even if no tax is due.
Calculate the Corporation Tax computation
Accounting profit is not automatically taxable profit. The computation adjusts it for items such as disallowable expenses, capital allowances and eligible losses. It then applies the relevant rates and reliefs: the small profits rate is 19% and the main rate is 25%, with marginal relief where applicable. Thresholds and other circumstances affect the result. For an online Company Tax Return, the accompanying computation must be iXBRL-tagged.
Prepare iXBRL accounts
Accounts submitted with an online return, where required, must also be iXBRL-tagged. That means financial facts are identified using the applicable reporting taxonomy, not merely displayed in a PDF. The accounts presentation depends on the company's reporting basis, such as FRS 105 micro-entity accounts or FRS 102 accounts. Our iXBRL accounts software guide explains how the tagging fits into a filing.
Include applicable supplementary pages
Some returns need supplementary pages alongside the main CT600. CT600A covers loans to participators of close companies; CT600E covers charities and community amateur sports clubs (CASCs). Support varies between products, so check the pages required before choosing a filing route. WeFile supports CT600A and CT600E, but not CT600B–D or CT600F–P. A page is included only when it applies to the company's circumstances.
Submit the return to HMRC
The software transmits the completed return through HMRC's Corporation Tax online filing service, using the company's Corporation Tax UTR and the filer's Government Gateway credentials. The electronic submission includes an IRmark, which identifies the submitted document for verification. Sending a return is not the same as its acceptance: HMRC's response must still be checked. For context on the move to commercial filing, read about the closure of HMRC's free service.
Handle Companies House filing separately
Filing statutory accounts with Companies House is a separate obligation with its own deadline and acceptance result. Not every CT600 product includes that submission; check its coverage before relying on a combined workflow. For supported company account types, WeFile prepares both submissions from one set of figures and tracks them separately. Charity and CASC filings in WeFile are CT600-only. See the Companies House filing software guide for the distinction.
Validate before sending
Useful checks include whether the balance sheet reconciles, profit and loss ties to reserves, required CT600 boxes are completed, and the submission meets relevant HMRC business rules. These checks can catch inconsistencies before transmission, but they cannot establish that every figure or tax treatment is correct. Validation reduces rejection risk; it cannot eliminate that risk or guarantee acceptance by either filing authority.
Track confirmation and records
After submission, keep the HMRC acknowledgement and submission receipt, and check whether any separate Companies House accounts filing was accepted or rejected. The two authorities report their outcomes independently; an accepted CT600 does not confirm acceptance of the accounts filing. Retain the return, supporting documents and responses with the company's records. Our CT600 submission guide explains what happens after sending.
WeFile combines these jobs for its supported filing routes. It appears on HMRC's Corporation Tax commercial software suppliers list, which indicates filing capability, not HMRC endorsement. Compare the coverage you need in our CT600 software comparison.
This information is general guidance, not professional tax or accounting advice.
Who files a CT600 and when is it due?
A CT600 is the Company Tax Return submitted to HMRC by UK limited companies and other entities within the charge to Corporation Tax for each accounting period when a return is required. This includes a dormant company if HMRC has issued a notice to deliver a return and has not withdrawn it. A nil tax bill does not cancel that obligation.
What is a Corporation Tax return?
It is the filing package sent to HMRC: the CT600 form, any relevant supplementary pages, statutory accounts where required, and the Corporation Tax computation. Accounts and computations submitted electronically are normally provided in iXBRL format. Read the Company Tax Return guide or follow our first-time CT600 guide.
Key deadlines and limits
- File the return: normally within 12 months of the accounting period end.
- Pay the tax: normally 9 months and 1 day after the period end; large companies may pay by quarterly instalments.
- Period length: a Corporation Tax accounting period cannot exceed 12 months.
- Late returns: for filing dates on or after 1 April 2026, the initial penalty is £200, rising to £400 after three months. A third consecutive late return raises those amounts to £1,000 and £2,000. Further tax-geared penalties can apply at six and twelve months.
Deadlines depend on your circumstances. See our Corporation Tax deadlines and penalties guide. This information is not professional advice.
HMRC's free CT600 service has closed — here's how to file now
HMRC's free Company Tax Returns online service, which let companies file a CT600 and basic accounts, closed on 31 March 2026. Returns are now generally filed using commercial software, either by the company or by an agent or accountant. Paper filing remains available only in the narrow circumstances HMRC sets out.
To get started, gather your Corporation Tax UTR, your own Government Gateway login and accurate accounts figures. If you are also filing eligible accounts with Companies House, you will need the company's authentication code.
WeFile appears on HMRC's Corporation Tax commercial software suppliers list. That listing describes filing capability, not an endorsement or accreditation. Read about the closure of HMRC's free filing tool or compare filing routes after the closure.
What WeFile handles: CT600, iXBRL accounts and tax computation
WeFile prepares the CT600 Version 3 Company Tax Return and its Corporation Tax computation from the figures you enter. For supported company account types, it also generates iXBRL-tagged statutory accounts and supports separate submissions to HMRC and Companies House. The relevant supplementary pages, tax adjustments and accounts presentation depend on the company's circumstances.
- CT600 Version 3
- Prepare the Company Tax Return and review its calculated tax figures.
- iXBRL-tagged accounts
- Generate supported FRS 105 micro-entity, FRS 102 Section 1A small-company, or full FRS 102 accounts.
- iXBRL tax computation
- Generate a Corporation Tax computation tagged with the relevant tax computation taxonomy.
- Rates and Marginal Relief
- Calculate applicable rates and relief, including financial-year apportionment and associated-company adjustments.
- Capital allowances
- Enter AIA, full expensing, main and special rate pool allowances, and structures and buildings allowance.
- Losses brought forward
- Apply eligible carried-forward losses, including the Part 7ZA deductions allowance restriction.
- CT600A
- Report s455 loans to participators, including directors’ loans and repayment relief. The s455 rate is 33.75% for relevant earlier loans and 35.75% for loans made on or after 6 April 2026.
- CT600E
- Enter supported charity and CASC exemption and supplementary-page information.
- Other filing routes
- Prepare dormant nil returns and amendments. A period of account over 12 months requires two Corporation Tax returns.
Not supported: CT600B–D, CT600F–P and audited accounts. Charity and CASC filings use a CT600-only route; WeFile does not file their accounts with Companies House.
How to file your CT600 online with WeFile
Start with the company and its accounting period, then enter or import reconciled financial figures. Choose the applicable accounts and filing route, review tax adjustments and any supplementary pages, and check the generated documents. Finally, authorise submission with your credentials and follow the separately tracked HMRC and Companies House results where both filings apply.
Add your company and confirm the accounting period
Add your company using its Companies House number, then confirm the Corporation Tax accounting period. Each CT600 covers no more than 12 months; a longer period of account is split into two returns.
Import or enter your figures
Import a trial balance from Xero, QuickBooks Online, FreeAgent or CSV, or enter your profit and loss and balance sheet figures. Check that the balance sheet balances and reconciles to the profit for the period.
Choose the accounts type and company status
Choose FRS 105 micro-entity accounts or FRS 102 accounts (Section 1A small company or full), and indicate whether the company is dormant, a charity or CASC, or a close company, as applicable.
Review tax adjustments and the computation
Add back disallowable expenses, claim capital allowances by pool—including AIA in box 690, main pool allowances in box 705 and special rate pool allowances—and apply losses brought forward. Review the computation: the small profits rate is 19%, the main rate is 25%, and marginal relief applies between £50,000 and £250,000, with those limits divided by the number of associated companies plus one.
Complete supplementary pages where relevant
Complete CT600A where s455 tax applies to directors’ loans or other loans to participators, or CT600E for a charity or CASC, where relevant.
Approve and submit
Enter the company’s Government Gateway credentials and, if filing accounts with Companies House, its authentication code. Approve and submit the CT600 Version 3 to HMRC with the applicable accounts and computation documents. For supported company accounts filings, submit iXBRL accounts to Companies House as a separate submission. Track each required submission and its receipt separately; charity and CASC filings are CT600-only.
WeFile CT600 pricing: pay per filing, no subscription
When comparing software, check the total cost and whether both HMRC and Companies House filings are included. See the CT600 software comparison and the guide to filing without an accountant, or see CT600 software prices compared.
Everything you need for corporation tax
Our CT600 filing software handles standard trading periods, dormant companies, and charities seamlessly. Please note that CT600B–D and CT600F–P are not supported. New to the Company Tax Return? Read our step-by-step CT600 guide before you file.
Everything in one submission
Prepare your CT600 version 3 for HMRC and iXBRL statutory accounts for Companies House from one workflow and one set of figures — the two submissions are sent and tracked separately.
Automatic tax computation
Our system calculates the 19% small profits rate, 25% main rate, and pro-rates marginal relief automatically across split financial years.
Capital allowances
Easily enter per-pool breakdowns mapped to the correct analysis boxes (690 AIA, 693 special rate allowance, 705 main pool, etc.).
Supplementary pages
Full support for supplementary pages CT600A (loans to participators) and CT600E (charities and CASCs).
Data import
Import a trial balance from Xero, QuickBooks Online, FreeAgent or CSV.
Automatic P&L, balance sheet & iXBRL
Profit and loss and balance sheet figures are totalled and reconciled, then iXBRL-tagged accounts and a tax computation are generated automatically for supported account types.
Amendments & repayments
Easily file an amended return or claim a repayment for an earlier period directly through our wizard.
See exactly what's covered
Our intelligent wizard supports the core requirements of most UK limited companies, automatically calculating complex relief structures, including full support for supplementary pages CT600A and CT600E.
Company & Return Info (Boxes 1–115)
What is iXBRL tagging and why does your CT600 need it?
Inline eXtensible Business Reporting Language (iXBRL) is human-readable HTML with machine-readable tags embedded in it. For online Company Tax Returns, HMRC generally requires both the accounts and tax computation to be submitted in iXBRL.
The computation is tagged against HMRC's Corporation Tax computational taxonomy. The accounts use the FRC's UK taxonomy: FRS 102 accounts are identified within it, as are FRS 105 micro-entity accounts. The tags tell the receiving system what each reported figure represents and which period it belongs to.
HMRC's supplier list distinguishes managed tagging and conversion services, which tag accounts prepared elsewhere, from software that generates iXBRL natively. WeFile generates tagged documents directly from the figures entered or imported for supported account types, so those filings do not need a separate tagging service.
Not every accounts format or entity type is supported. Limited exceptions to iXBRL accounts submission also exist, including for some entities not required to prepare Companies Act accounts. For WeFile charity and CASC filings, the HMRC workflow can instead include an uploaded accounts PDF with an explanation; WeFile does not e-file their accounts to Companies House.
Read GOV.UK's XBRL guide for UK businesses and HMRC's Corporation Tax commercial software suppliers list. Inclusion on a supplier list is not an endorsement or certification.
From P&L and balance sheet to tagged accounts, automatically
For a supported small UK limited company, the figures flow through one filing workflow rather than being re-keyed for each document.
Bring in your figures
Enter figures in the wizard or import a trial balance from Xero, QuickBooks Online, FreeAgent or a CSV export. The imported or entered figures form the starting point for the accounts and return, without entering them again in a separate tagging tool.
Calculate and reconcile the profit and loss and balance sheet
WeFile totals the P&L, carries profit after tax into retained earnings and requires the balance sheet to balance before you continue. A reserves-movement check also flags when closing retained earnings differ from opening retained earnings plus profit. Dividends are a common explanation; that check is information, not an error.
Calculate Corporation Tax from the same figures
The calculation accounts for the applicable 19% or 25% rates, Marginal Relief, associated companies, capital allowances and periods spanning financial years. The resulting tax charge feeds back into the P&L and balance sheet.
Choose the appropriate accounts presentation
WeFile identifies the applicable supported micro-entity (FRS 105) or small-company (FRS 102 Section 1A or full) presentation. FRS 105 collapses fixed assets and capital and reserves on the face of the balance sheet and does not permit fair value accounting. FRS 102 can present items such as intangible assets and share premium separately. Learn how WeFile detects the account type.
Apply the tags automatically
WeFile applies taxonomy elements and period contexts to current-year and comparative figures, including supported dimensional items such as share premium and capital allowance pools. It also labels documents and disclosures, including full or filleted accounts, audit exemption statements and the director's name.
Use one set of figures for two submissions
For supported limited-company filings with both legs, the generated accounts document is sent to Companies House and attached to the CT600 and computation sent to HMRC. HMRC always receives the P&L; where permitted, you can choose filleted accounts for Companies House. HMRC and Companies House validate submissions on receipt. WeFile shows each response, including acceptances, rejections and error codes, so you can correct and resubmit where needed.
Preparing the underlying numbers? See our guide to how to fill in the balance sheet and profit and loss.
Automated iXBRL tagging vs manual entry and conversion
The right route depends on where your accounts are prepared and whether your entity and supplementary pages are supported.
| Consideration | WeFile (native tagging) | Accounts prepared elsewhere + tagging/conversion service | Manual re-keying into separate CT600 software |
|---|---|---|---|
| Where figures are entered | Once in the wizard or through an import. | In your accounts package. | In the accounts package and again in CT600 software. |
| How iXBRL tags are applied | Automatically for supported documents and account types. | By a third party or conversion tool; the result needs review. | Depends on the separate software used. |
| Consistency between accounts, computation and CT600 | Generated from one set of figures. | Depends on the figures matching across products. | Transcription differences are possible. |
| Balance sheet reconciliation | Must balance before continuing. | Checked in the accounts package. | Your responsibility across the separate products. |
| Corporation Tax calculation | Calculated automatically from the filing figures. | Handled separately from the tagging service. | Depends on the CT600 software. |
| Extra service or cost for tagging | None for supported account types. | Often a separate fee. | Varies by software. |
| Main risk or limitation | Unsupported entities or supplementary pages, including CT600B–D and CT600F–P, need another route. | Tag or figure mismatches between documents. | Typing errors can cause rejections or incorrect returns. |
What can go wrong without automated tagging
- CT600 figures that do not match the tagged accounts.
- Missing or incorrect tags or period contexts that lead to an HMRC rejection.
- The wrong taxonomy or accounts-type label.
- Micro-entity accounts containing items FRS 105 does not permit.
- An unbalanced balance sheet reaching submission.
Automation reduces these risks, but it cannot establish whether your underlying figures are correct. Directors remain responsible for the accuracy of the return and accounts.
HMRC-recognised CT600 software: what that means for your filing
WeFile appears on HMRC's Corporation Tax commercial software suppliers list . Suppliers on that list have given HMRC evidence that their software or service is capable of producing one or more elements of a Company Tax Return.
The list distinguishes several categories of capability, including software that produces and submits the CT600 itself, software that submits iXBRL accounts and computations, tools aimed at self-filers, products offering integrated iXBRL tagging, and separate managed tagging or conversion services for accounts prepared elsewhere.
HMRC is explicit that it cannot recommend or endorse one product over another, does not test the security of supplier software, and that inclusion on the list is not an approval, accreditation or certification of any kind.
Since the joint HMRC/Companies House "File your accounts and Company Tax Return" service closed on 31 March 2026 , Company Tax Returns filed from 1 April 2026 onward generally require commercial software such as WeFile.
Who needs to file a CT600 and when?
The obligation to file is triggered when HMRC issues a Notice to deliver a Company Tax Return . A return can still be required even where the company made a loss or has no tax to pay — there is no general turnover threshold that removes an issued notice-to-deliver obligation.
| Obligation | Normal deadline |
|---|---|
| Company Tax Return (CT600) | 12 months after the accounting period ends |
| Corporation Tax payment | 9 months and 1 day after the accounting period ends |
A Corporation Tax accounting period cannot exceed 12 months. If your statutory accounts cover a longer period — such as an 18-month first year — you must file two separate Company Tax Returns covering it.
A dormant company can normally stop filing Company Tax Returns after telling HMRC it's dormant, but must still file for any period where HMRC has issued and not withdrawn a notice to deliver. Companies House annual accounts remain a separate obligation regardless of dormancy status for Corporation Tax.
Marginal Relief and the April 2023 Corporation Tax rate changes
For non-ring-fence profits arising on or after 1 April 2023, the small profits rate of 19% applies at £50,000 or less, the main rate of 25% applies above £250,000, and Marginal Relief generally tapers the effective rate for profits between those limits.
The standard Marginal Relief fraction is 3/200. HMRC's formula for the relief is:
Marginal Relief = (F × (U − A)) × (N ÷ A)- F — the Marginal Relief fraction (3/200)
- U — the upper profits limit (normally £250,000)
- A — augmented profits (taxable total profits plus exempt distributions received)
- N — taxable total profits
Both the £50,000 and £250,000 thresholds are reduced pro-rata for accounting periods shorter than 12 months, and are divided by one plus the number of associated companies. Financial-year apportionment can also apply where a period straddles a rate change. Because of this, not every company with profits between the raw thresholds automatically qualifies for relief at the same rate — it depends on augmented profits and associated-company counts.
WeFile automatically calculates the applicable Corporation Tax rate and any Marginal Relief due, including associated-company adjustments and short or split-period apportionment, as part of its tax computation.
Source: GOV.UK Corporation Tax rates and allowances and HMRC Company Taxation Manual CTM03925 .
Filing CT600 and annual accounts together: dual submission to HMRC and Companies House
The Company Tax Return and the annual accounts are two separate statutory filings, sent to two separate bodies, each with its own acceptance response. HMRC receives the CT600, the tax computation and supporting accounts; Companies House separately receives the annual accounts required under company law.
Suitable software can generate and submit both filings from a single set of figures, but accepting one does not satisfy the other — filing your CT600 does not file your Companies House accounts, and vice versa, so both legs still need to be tracked and confirmed independently.
WeFile offers dual submission — sending the CT600 to HMRC and the statutory accounts to Companies House — for supported limited-company account types, and tracks the status of each leg separately so you can see exactly which has been accepted.
Charity, CASC and non-Companies-House entity filings are CT600-only in WeFile — the accounts leg must be handled separately for those entities — and not every CT600 supplementary page or accounts presentation is supported.
See GOV.UK's guidance on preparing and filing annual accounts and our detailed walkthrough on filing CT600 and Companies House accounts together.
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Dormant Company
- Companies House Filing
- CT600 Nil Return
- Generated iXBRL Accounts
Trading Company
- Full CT600 Return
- Companies House Accounts
- CT600A and CT600E Support
- Auto Tax Calculation
Accountant Membership
- Up to 100 Filings
- Priority Support
- Client Management
- All Filing Types Included