Small company CT600

CT600 software for small limited companies: what to check before you file.

Small company Corporation Tax can still involve iXBRL accounts, computations, director loans, capital allowances, losses, and supplementary pages. Use software that helps you review the whole filing package.

Small does not always mean simple

Many UK limited companies have a small team, one or two directors, and straightforward trading activity. That does not make the Company Tax Return a simple confirmation statement. The CT600 still needs to match the accounting period, accounts, computation, claims, reliefs, and filing attachments.

The closure of the joint HMRC and Companies House filing service has made this more visible. Companies that previously used the old route now need commercial software for HMRC Company Tax Return filing.

What the software needs to cover

HMRC says companies should file Company Tax Returns online using commercial software. A small limited company should look for software that handles the full return package, not just a single CT600 screen.

  • main CT600 preparation for the accounting period;
  • Corporation Tax computation and tax-adjusted profit;
  • accounts and computation attachments in the required electronic format;
  • capital allowances, losses, reliefs, and credits where relevant;
  • supported supplementary pages for specialist facts;
  • validation checks before Government Gateway submission;
  • evidence of the submitted return and HMRC response.

Common small-company review areas

A small company return often goes wrong because an everyday bookkeeping item has Corporation Tax consequences. Good software should make those areas easy to spot.

  • Director loans: overdrawn loan accounts may create CT600A and section 455 review points.
  • Capital allowances: asset purchases need treatment in the tax computation, not only in the accounts.
  • Losses: brought-forward, current-year, carried-back, group, or carried-forward losses need clear choices.
  • Disallowable costs: accounting expenses are not always deductible for Corporation Tax.
  • Interest and finance costs: simple cases may be straightforward, but related-party and group cases need care.
  • Claims and credits: R&D, creative industry, or other specialist claims can change the filing package.
  • Late or amended returns: rejection, amendment, and penalty risk should be visible in the workflow.

Accounts filing and CT600 filing are connected but different

Companies file accounts with Companies House and the Company Tax Return with HMRC. The numbers are connected, but the tax return may include adjustments that do not appear as the same figures in the statutory accounts.

A good workflow keeps the relationship clear: accounts support the return, the computation explains the tax adjustments, and the CT600 reports the result. If the product only asks for final tax payable, it is probably too thin for review.

What small companies should prepare first

Choosing software is easier when you know the return you need to file. Prepare the file before you start entering CT600 figures.

  • company accounts and bookkeeping records for the period;
  • Companies House filing status and HMRC accounting period;
  • company UTR and Government Gateway access or agent details;
  • profit and loss, balance sheet, fixed asset register, and loan accounts;
  • details of asset purchases, disposals, and capital allowance claims;
  • losses, reliefs, repayments, or credits claimed;
  • dividends, payroll, director loan movements, and connected-party balances;
  • any overseas, group, property development, charity, or creative industry facts.

Buyer questions for small-company CT600 software

A small company should not have to buy an enterprise tax suite, but it does need enough structure to file accurately.

  • Does the product explain how accounting profit becomes taxable profit?
  • Can it handle iXBRL accounts and computation attachments?
  • Does it support the supplementary pages that small owner-managed companies commonly need?
  • Can a director review the return before filing?
  • Does it preserve submission evidence and HMRC responses?
  • Can an accountant step in if the return becomes more complicated?
  • Is pricing practical for one filing without blocking future practice support?

How Robocount fits small limited companies

Robocount is focused on UK Corporation Tax and CT600 filing. It is built for directors who want to file a company return themselves, and for accountants who need a repeatable workflow for small-company clients.

  • Browser-based CT600 preparation and review.
  • Workflow around computations, iXBRL attachments, and supported supplementary pages.
  • Owner-managed-company review points, including directors' loans and supplementary-page triggers.
  • Government Gateway filing workflow for supported returns.
  • API and AI-assisted routes for structured data collection and review.

FAQ

Can a small limited company file its own CT600?

Yes, if it uses suitable software and the director is comfortable reviewing the return. Accountant help is sensible where the accounts, claims, loans, losses, or specialist facts are not straightforward.

Do micro-entity accounts make the CT600 easy?

Not automatically. Micro-entity accounts can still need a Corporation Tax computation, iXBRL attachment handling, adjustments, and supplementary-page review depending on the company's facts.

Do small companies need iXBRL?

HMRC guidance says company returns must be filed electronically and that computations and accounts must be in Inline XBRL format, subject to the detailed rules and exceptions in current guidance.

What is the biggest small-company CT600 mistake?

Treating the CT600 as only a tax payable number. The return package needs accounts, computations, attachments, supplementary-page decisions, and evidence that the director approved the final position.

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.