A CT600 is the corporation tax return a UK company files with HMRC for an accounting period. It is how the company reports its tax position for that period. It sits alongside your statutory accounts, not instead of them.
This guide is general information. Filing dates, exemptions and computations depend on your facts. A qualified accountant should prepare or review anything you submit.
YearReady™ helps you assemble a clean year-end pack early so CT600 work is not a last-minute reconstruction. Alfred prepares findings. A qualified professional signs off anything regulated.
CT600 versus Companies House accounts
Owners often treat "year-end" as one job. In practice there are two related filings:
- Companies House accounts: the statutory accounts on the public record (with size-based options for how much detail you publish).
- CT600 to HMRC: the corporation tax return for the same accounting period, usually with tax computations.
Missing either can create separate problems. Late Companies House accounts attract automatic civil penalties. Late corporation tax returns and payments have their own HMRC consequences. See the UK year-end accounts checklist for the full prep list.
When the CT600 is usually due
For most companies, the corporation tax return for an accounting period is due within 12 months of the end of that period. Corporation tax payment dates can be earlier than the return deadline, depending on your size and circumstances. Do not assume "I have a year to file" means "I have a year to pay". See corporation tax payment deadline UK. Confirm both dates with your accountant.
What usually goes into the pack
Final accounts for the period (or draft accounts your accountant will finalise).
Tax computations showing how accounting profit becomes taxable profit.
Capital allowance and relief workings where relevant.
Brought-forward losses and other history from prior periods.
Supporting schedules your accountant asks for (director's loan, fixed assets, stock).
Who prepares and who submits
Many small companies ask their accountant to prepare the CT600 and submit it. Some software-led processes still need a human to approve figures. Ask Alfred™ does not claim to submit your CT600. Alfred helps you get ready earlier; a qualified professional handles regulated filing judgement and submission where your process requires it.
How this ties to year-end readiness
A messy director's loan, unreconciled bank, or missing invoices slows both accounts and the CT600. Fix those early. Related reading: What is a director's loan account, Companies House late filing penalties, and Micro-entity versus small company accounts.
Quick CT600 checklist
- Confirm the accounting period dates match Companies House and HMRC.
- Diary the return deadline and any tax payment dates separately.
- Send a labelled year-end pack to your accountant early.
- Review draft computations before anything is submitted.
- Store the submitted return, computations and accounts together for next year.
What to read next
- Corporation tax payment deadline UK
- UK year-end accounts checklist
- YearReady™
- Confirmation statement deadline
- All guides
This page is general information for UK companies. Rules, thresholds and deadlines can change. Nothing here is regulated advice, and nothing regulated should be submitted without a human approval from a qualified professional. Prefer current GOV.UK guidance for your obligations.