Corporation Tax deadlines
When CT600 returns and Corporation Tax payments are due. Filing deadline is 12 months after period end; payment is 9 months and 1 day.
Quick answer
- Companies House annual accounts: due 9 months after company year end (first year: 21 months from incorporation)
- Corporation Tax payment: due 9 months and 1 day after company year end
- CT600 return: due 12 months after company year end
- Confirmation statement: due once a year, 14-day filing window
The four key dates
Limited companies have four recurring deadlines tied to their accounting period and to Companies House. Miss any and penalties apply automatically.
1. Companies House annual accounts
File annual accounts with Companies House within 9 months of the end of your company's accounting period. For your first set of accounts, the deadline is 21 months from incorporation (because the first period can be longer).
Late filing triggers automatic Companies House penalties starting at £150 and rising sharply.
2. Corporation Tax payment
Pay Corporation Tax to HMRC 9 months and 1 day after the end of your accounting period. So for a year ending 31 March, payment is due by 1 January.
For very large companies (profits over £1.5m or £20m for groups), payments are made in quarterly instalments.
3. CT600 company tax return
File the CT600 with HMRC within 12 months of the end of your accounting period. So if your year ends 31 March 2025, the CT600 is due by 31 March 2026.
Note: payment is due before the return — 9 months and 1 day vs. 12 months for filing. Companies should still file as early as practical to know exactly what they owe.
4. Confirmation statement
File a confirmation statement at Companies House at least once every 12 months. The 14-day filing window starts from your statement date. Failing to file is a criminal offence and can lead to the company being struck off.
What happens if you miss them
- Late accounts at Companies House: £150 then £375 then £750 then £1,500 (private companies); doubled if you're late two years running
- Late CT600: £100 immediate, another £100 at 3 months, then 10% of unpaid tax at 6 months, plus another 10% at 12 months
- Late Corporation Tax payment: daily interest from day one at HMRC's published rate
- Late confirmation statement: can lead to strike-off action
Stay on top
- Diary all four dates as soon as your accounting period is fixed
- File accounts early to give yourself buffer for revisions
- Set up reminders 60, 30, and 7 days before each deadline
- If you can't make a deadline, contact HMRC or Companies House before the deadline — appeals are easier than after-the-fact
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