What a Company Tax Return actually contains
People say “the CT600” but the return is three things together:
- The CT600 form — the return itself, summarising income, profit and the tax due
- Tax computations — showing how taxable profit was worked out from the accounting profit (adding back disallowables, claiming capital allowances and reliefs)
- Statutory accounts — the company’s financial statements for the period
All of it is filed online with HMRC in iXBRL format.
CT600 vs your Companies House accounts
A frequent confusion: the CT600 is not the same as your Companies House filing. Your annual accounts go to Companies House (small companies can file a reduced ‘filleted’ set). The CT600, with full accounts and computations, goes to HMRC to assess tax. Two filings, two bodies, same underlying numbers.
The iXBRL hurdle
HMRC requires the accounts and computations to be tagged in iXBRL so its systems can read the figures. Proper accounts and tax software does the tagging automatically — but it’s a real barrier for anyone trying to file by hand, and one reason most companies use software or an accountant for the CT600.
Deadlines
- CT600 return: 12 months after the accounting period ends
- Corporation Tax payment: 9 months and 1 day after the period ends (before the return)
- First year: usually two CT600s, because the first period runs over 12 months
We prepare and file it with your accounts
We build the computation, complete the CT600, tag everything in iXBRL and file it with HMRC alongside your accounts — a fixed £399 + VAT for micro-entity companies. Call 0114 327 1480.