Example

Worked example

Period start: 1 January 2025; Period end: 31 March 2026; Profit: £150,000; First accounts: yes. Enter your own details to replace this example.

Accounts from 1 January 2025 to 31 March 2026 (15 months) need two CT600 returns: 1 January 2025 to 31 December 2025, with tax due 1 October 2026, and 1 January 2026 to 31 March 2026, with tax due 1 January 2027. File both by 31 March 2027. By days, £150,000 profit splits £120,329.67 and £29,670.33.

Accounts (period of account)

1 January 2025 to 31 March 2026 (455 days, 15 months)

First accounting period (CT600 1)

1 January 2025 to 31 December 2025 (365 days)

First period's share of the profit (365/455 days)

£120,329.67

First period: pay Corporation Tax by

1 October 2026

Second accounting period (CT600 2)

1 January 2026 to 31 March 2026 (90 days)

Second period's share of the profit (90/455 days)

£29,670.33

Second period: pay Corporation Tax by

1 January 2027

File both CT600 returns by

31 March 2027

Companies House accounts deadline

1 October 2026

• A Corporation Tax accounting period can't be longer than 12 months, so accounts covering more are split into the first 12 months and the rest, each with its own CT600 and computation (CTA 2009 s.10). The same accounts go with both returns.
• Trading profits are split by the number of days in each period (CTA 2009 s.52). The first period's share is rounded to the nearest penny and the second period gets the rest, so the two add up to the total exactly.
• Capital allowances are worked out separately for each period, and the Annual Investment Allowance is reduced for a period shorter than 12 months.
• Chargeable gains are not split by days: a gain belongs to the period in which the disposal happens.
• Each period is taxed at the rates for the financial years (1 April to 31 March) it falls in, and the small profits and marginal relief limits are reduced for a period shorter than 12 months.
• Both returns are due 12 months after the end of the accounts (Finance Act 1998 Sch 18 para 14), or 3 months after HMRC's notice to file if that is later. If you lengthened the year, tell HMRC the new accounting period dates before the original filing deadline.
• For first accounts we take the start date as the date of incorporation. If the company started trading later, its first Corporation Tax accounting period starts when it began trading, which changes the split: HMRC writes to confirm the dates.
• Payment dates assume the company doesn't pay Corporation Tax by quarterly instalments (large companies).

Sources: GOV.UK: Accounting periods for Corporation Tax · Corporation Tax Act 2009, section 10 (end of an accounting period) · Corporation Tax Act 2009, section 52 (apportioning trade profits by days) · Finance Act 1998, Schedule 18, paragraph 14 (filing date) · GOV.UK: Pay your Corporation Tax bill · Companies House: Life of a company — accounts (filing deadlines)