When to file in iXBRL
Two regulators, two independent clocks, both counting from your financial year end but landing on different dates.
| Filing | Deadline |
|---|---|
| Companies House accounts (private company) | 9 months after financial year end |
| Companies House accounts (public company) | 6 months after financial year end |
| CT600 (Company Tax Return) | 12 months after accounting period end |
| Corporation Tax payment | 9 months and 1 day after accounting period end (most companies) |
| First Companies House accounts | 21 months from incorporation (a different rule — see below) |
Your first year is a special case
A company's very first set of Companies House accounts is generally due 21 months from incorporation, not 9 months from a year end — a rule that catches out a lot of first-time filers. See our startups guide.
Miss a deadline, and the clock doesn't stop
Late filing penalties escalate the longer a filing stays outstanding — under both regimes independently. See our late filing penalties update.
Use the calculator
Enter your financial year end and company type in our free deadline calculator for both estimated dates at once.
Frequently asked questions
Are the CT600 and Companies House deadlines ever the same date?
They can coincide depending on your specific dates, but they're calculated independently — 12 months from accounting period end for CT600, versus 9 or 6 months from financial year end for Companies House. Don't assume one covers the other.
What if my first accounting period is longer than 12 months?
A CT600 accounting period can't exceed 12 months, so an extended first year needs two separate CT600 returns — one for the first 12 months, one for the remaining days.
Can I get an extension on either deadline?
Extensions are possible in limited circumstances through Companies House, but aren't guaranteed and need to be requested before the deadline passes — check directly with Companies House or HMRC rather than assuming one is available.
Deadline coming up?
Send your accounts over — we typically turn tagging around within 24 hours.
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