Corporation Tax deadlines: when does a UK company pay and file?

For most UK limited companies, Corporation Tax must reach HMRC 9 months and 1 day after the end of the accounting period. A company with a 31 March 2026 year end pays by 1 January 2027; a 30 June 2026 year end pays by 1 April 2027; a 31 December 2026 year end pays by 1 October 2027.

This payment date applies to small and medium companies, which covers nearly every owner-managed business. HMRC does not send a bill first, so the company has to work out its liability, usually from the draft accounts and tax computation, and pay using its 17-character Corporation Tax payment reference.

The Company Tax Return (form CT600), with the accounts and tax computation, must be filed online 12 months after the end of the accounting period. A 31 March 2026 year end therefore files by 31 March 2027.

Because the payment date comes three months before the filing date, the tax is normally paid before the return is submitted. In practice, preparing the accounts and CT600 together, well before the payment date, is the only reliable way to know the right figure to pay.

Large companies, broadly those with taxable profits above £1.5 million a year, pay by quarterly instalments instead of a single payment. For a 12-month period, instalments are due 6 months and 13 days after the period starts and then every 3 months, which is the 14th day of months 7, 10, 13 and 16. For a period starting 1 April 2026, that means 14 October 2026, 14 January 2027, 14 April 2027 and 14 July 2027.

The £1.5 million threshold is divided between associated companies and reduced for short periods. A company does not normally need to pay instalments in the first year it becomes large if its profits are no more than £10 million and it was not large in the previous year. Very large companies, with profits above £20 million, pay even earlier, in months 3, 6, 9 and 12.

HMRC charges a £100 penalty if the CT600 is 1 day late, and another £100 if it is 3 months late. If the return is 6 months late, HMRC estimates the tax due and charges a further penalty of 10% of the unpaid tax; at 12 months late, another 10% of any tax still unpaid is added.

If a return is late three times in a row, the two £100 penalties each increase to £500. These are HMRC penalties; Companies House charges its own, separate late filing penalties for late accounts.

Late payment interest starts from the day after the payment deadline and runs until HMRC receives the money. Since 6 April 2025 HMRC's late payment interest rate has been the Bank of England base rate plus 4%, so the cost moves with the base rate. HMRC also pays a lower rate of repayment interest on tax paid early or overpaid.

If the company cannot pay in full, contact HMRC before the deadline about a Time to Pay arrangement. Interest still runs, but an agreed plan avoids enforcement action. We can prepare the figures HMRC asks for; this is technical work, booked through our paid advice service.

A trading company draws up accounts for the 12 months to 31 March 2026 and has taxable profits of £40,000 and no associated companies. As profits are below £50,000, the small profits rate of 19% applies, giving Corporation Tax of £7,600.

Its deadlines are: Corporation Tax of £7,600 paid by 1 January 2027; Companies House accounts filed by 31 December 2026; and the CT600, accounts and computation filed with HMRC by 31 March 2027. If the CT600 were filed on 1 April 2027, a £100 penalty would apply immediately, and interest would run on any part of the £7,600 not paid by 1 January 2027.