Home / Questions / What Is a CT600?
Last updated 23 October 2026. Written by the Limited Company Accountant UK team, part of Accotax. Figures are for the 2026/27 tax year; always check GOV.UK for the latest rates.
Short answer: A CT600 is the Company Tax Return you file with HMRC to report your profits and calculate Corporation Tax. It is due 12 months after your accounting period ends.
At a glance
| Due | 12 months after year end |
|---|---|
| Filed with | HMRC online |
| Includes | Accounts and tax computation |
What goes in it
Your profit, adjustments, allowances, reliefs and the tax due. Accounts and computations are attached in iXBRL format.
Even with no tax
You must file a return even if you owe nothing.
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The bottom line
A CT600 is the Company Tax Return you file with HMRC to report your profits and calculate Corporation Tax. If you would rather not do it alone, our fixed fees start at £45.83 + VAT a month.
Frequently asked questions
Who files the CT600?
The company, usually through its accountant.
What if I miss it?
Penalties start at £100 and increase.
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