What are the corporation tax deadlines?
A UK company has two corporation tax deadlines for each accounting period, plus a separate deadline at Companies House. For companies with taxable profits up to £1.5 million, GOV.UK’s Pay your Corporation Tax bill and Company Tax Returns guides set them as:
| Deadline | When | Who it’s with |
|---|---|---|
| Pay corporation tax | 9 months and 1 day after the period ends | HMRC |
| File the CT600 | 12 months after the period ends | HMRC |
| File annual accounts | 9 months after the accounting reference date | Companies House |
The CT600 is only required if HMRC has sent the company a notice to deliver a Company Tax Return, which almost every trading company receives.
What are the dates for common year ends?
Months are counted to the corresponding date. A month-end year end runs to the last day of the target month.
| Year end | Accounts due (CH) | Tax payment due | CT600 due |
|---|---|---|---|
| 31 March 2026 | 31 December 2026 | 1 January 2027 | 31 March 2027 |
| 30 June 2026 | 31 March 2027 | 1 April 2027 | 30 June 2027 |
| 30 September 2026 | 30 June 2027 | 1 July 2027 | 30 September 2027 |
| 31 December 2026 | 30 September 2027 | 1 October 2027 | 31 December 2027 |
The deadline planner on the FileMyLtd homepage works out these dates for any year end. A company’s first Companies House deadline is different: 21 months after incorporation, or 3 months after the first accounting reference date if that’s later.
Why is the tax due before the return?
The two dates are set separately, and HMRC treats the payment date as the one that matters for interest. From 9 months and 1 day, HMRC charges late payment interest on any unpaid tax, even though the return isn’t due for another three months.
In practice that means the accounts and the tax computation need to be finished within nine months, not twelve. A company that waits for the CT600 deadline to work out its tax will usually pay interest.
What are the penalties for a late CT600?
HMRC’s late filing penalties doubled for returns with a filing date on or after 1 April 2026, under section 265 of the Finance Act 2026:
| How late | Penalty |
|---|---|
| 1 day | £200 |
| 3 months | another £200 |
| Third late return in a row | £1,000 (£2,000 if over 3 months late) |
| 6 months | HMRC estimates the tax and adds 10% of the unpaid tax |
| 12 months | another 10% of the unpaid tax |
A tax determination issued at six months can’t be appealed. The company has to file its return, which replaces the estimate. Appeals against penalties need a reasonable excuse, and the return must be filed first.
Companies House fines late accounts separately, from £150. The late filing penalties guide covers those.
What happens if the period crosses 1 April?
Corporation tax rates apply by financial year, which runs from 1 April to 31 March. If an accounting period straddles 1 April, the profit is split by days between the two financial years. The rates have been the same since April 2023, 19% to 25% with marginal relief in between, so the split rarely changes the bill for now. The corporation tax calculator works out the tax for the year from 1 April 2026.
What do you need ready before the payment date?
- the company’s accounts for the period, finished and agreed;
- the tax computation, including any adjustments and capital allowances;
- the company’s 10-digit UTR, which is the payment reference. The UTR guide explains how to find it.
The deadline most often missed
UK searches for “corporation tax deadline” run at about 720 a month, and “corporation tax payment deadline” at about 480 (DataForSEO, November 2026). Only 50 a month search for “ct600 deadline”. That pattern suggests directors think about corporation tax as a payment first and a return second, which is the right order: the payment is due three months earlier, and interest starts from the day after.
Sources
- Company Tax Returns (GOV.UK), updated 30 September 2026. Checked 6 November 2026.
- Pay your Corporation Tax bill (GOV.UK), updated 28 October 2026. Checked 6 November 2026.
- Finance Act 2026, section 265 (legislation.gov.uk), updated checked 6 November 2026. Checked 6 November 2026.
- Increases to Corporation Tax late filing penalties (HMRC), updated 26 November 2025. Checked 6 November 2026.
Search figures are 12-month UK averages from DataForSEO (Google Ads data), pulled 6 November 2026. Spotted something out of date? Tell us and it will be corrected.