Why commercial software is now the normal route

GOV.UK says the service for filing accounts and the Company Tax Return together closed on 31 March 2026. It also says companies should file Company Tax Returns online using commercial software, with paper filing limited to narrow cases such as a reasonable excuse or filing in Welsh.

That is a practical change for many directors and a commercial change for accountancy practices. The CT600 is no longer a lightweight end-of-year online form for companies that previously used the joint service. It is a filing package that needs the right software workflow.

What a Company Tax Return actually includes

HMRC describes a Company Tax Return as the CT600, any supplementary pages, company accounts, and tax computations. For online filing, accounts and computations commonly need Inline XBRL tagging. That means the software decision should not be based only on whether a screen can produce a main CT600 form.

A useful commercial Corporation Tax product should make the whole package visible:

the main CT600 for the right accounting period;
Corporation Tax computations and relief calculations;
accounts and computation attachments in the required electronic format;
supplementary pages where the company has specialist facts;
validation before submission;
Government Gateway submission status and response handling;
a durable review trail for the person signing or approving the return.

Buyer checklist for CT600 software

Before choosing a product, decide what kind of return you need to file. A dormant company, a simple trading company, a close company with an overdrawn director's loan account, and a company claiming R&D or creative industry relief do not all need the same depth of workflow.

Filing scope: Can the product prepare and submit the CT600 elements you need, not only accounts?
Supplementary pages: Does it support the pages that match your facts, such as CT600A, CT600C, CT600L, CT600N, or CT600P?
iXBRL: Can it produce or accept tagged accounts and computations suitable for the return package?
Review workflow: Can an accountant, director, or agent see why the numbers reached the return?
Corrections: Does the workflow make rejected returns, amendments, and resubmissions manageable?
Team use: For practices, can preparers and reviewers work without seat-count friction?
Automation: For AI or API-led work, is there a structured route rather than copy-paste into forms?

Common gaps to avoid

The first gap is treating accounts filing and Corporation Tax filing as the same problem. Companies House accounts and the HMRC Company Tax Return are connected, but they are not identical. A director can still need separate review for tax adjustments, losses, loans to participators, capital allowances, and supplementary pages.

The second gap is choosing software that covers a "simple" return but leaves no route for edge cases. Owner-managed companies often look simple until a director's loan account, group relationship, R&D credit, creative industry claim, or property development activity changes the CT600 package.

The third gap is weak evidence. The return may be filed online, but the reviewer still needs to know what was included, what was excluded, which source figures were used, and which HMRC references were checked.

What accountants should standardise

Practices should treat the post-closure software shift as a chance to standardise CT600 intake. A repeatable workflow is faster than a last-minute scramble through accounts, spreadsheets, portal exports, and filing forms.

Capture company, accounting period, UTR, filing deadline, and agent authority status early.
Map trial balance and accounts figures to the computation and CT600 review points.
Use a supplementary-page checklist before assuming the return is straightforward.
Keep review notes for judgment areas such as loans, losses, capital allowances, and claims.
Separate preparation, review, client approval, and submission status.

What directors should prepare

Directors moving from the old service should prepare the source data before the deadline. Software cannot fix missing accounts, unclear director loan movements, or unresolved tax adjustments at the last minute.

company accounts for the period;
profit and loss, balance sheet, and tax adjustment detail;
capital allowance additions and disposals;
losses brought forward or claimed;
directors' loan account movements and repayments;
details of reliefs, credits, or specialist activities;
Government Gateway access or accountant authorisation.

How Robocount approaches commercial Corporation Tax software

Robocount is built as UK Corporation Tax software rather than a general accounts product with a CT600 form attached. The workflow is designed around preparation, review, validation, and filing of the Company Tax Return package.

Browser-based CT600 preparation for accountancy practices and company directors.
Supported CT600 supplementary pages connected to the main return.
Computation, iXBRL, and filing readiness handled as part of one review flow.
Government Gateway submission workflow for supported returns.
API and MCP-native surfaces for structured automation and AI-assisted filing workflows.

FAQ

Do all companies need commercial Corporation Tax software?

GOV.UK says you should file your Company Tax Return online using commercial software. Paper CT600 filing is limited to specific cases, such as a reasonable excuse or filing in Welsh.

Is accounts software enough for CT600 filing?

Not necessarily. Accounts software may help prepare accounts, but the Company Tax Return also includes the CT600, computations, supplementary pages where needed, and HMRC online filing requirements.

What changed after 31 March 2026?

The joint service for filing accounts and Company Tax Returns together closed on 31 March 2026. From 1 April 2026, companies need another filing route, usually commercial software.

Can Robocount help accountants as well as directors?

Yes. Robocount is designed for both practice-led and director-led CT600 work, with a structured workflow for the return package rather than a one-off form.

Useful official references

This guide is general product and filing workflow information, not tax advice. Check current GOV.UK guidance and the company's facts before filing.

Commercial Corporation Tax software: what UK companies need after the HMRC service closure.