Definition
The CT600 is the Company Tax Return form a company files with HMRC for each Corporation Tax accounting period. It is filed online with the company's accounts and tax computation, and is due 12 months after the period ends.
What is filed
A Company Tax Return is more than the form. It is made up of:
- the CT600 itself, a set of numbered boxes summarising income, reliefs and the tax due;
- the company’s accounts, tagged in iXBRL;
- the tax computation, also in iXBRL;
- any supplementary pages that apply, such as CT600A for loans to directors or CT600L for research and development.
A return cannot cover more than 12 months. A longer period of account is split into two accounting periods, each with its own CT600.
Deadline and penalties
The return is due 12 months after the end of the accounting period. The tax itself is due earlier, usually 9 months and 1 day after the period ends.
| How late | Penalty |
|---|---|
| 1 day | £100 |
| 3 months | Another £100 |
| 6 months | HMRC estimates the bill and adds 10% of the unpaid tax |
| 12 months | Another 10% of the unpaid tax |
A return can normally be amended up to 12 months after its filing deadline.
Read more: The CT600 box by box, Submitting your Corporation Tax return and Amending a CT600.