UK Corporation Tax Deadlines & Penalties (2026 Guide)
Corporation Tax is not billed by HMRC. Your company works out its own tax, pays it, and reports it on a Company Tax Return. Because payment falls due before the return, many directors miss one of the two dates and only find out when a penalty notice arrives.
The cost of missing the return deadline has also risen recently. HMRC doubled its fixed late filing penalties for returns due on or after 1 April 2026, so an overdue CT600 is more expensive than it was a year ago.
This guide explains when Corporation Tax is due, when the CT600 must be filed, how penalties and interest work, and how to appeal. It also covers the 2026 changes that affect how returns are filed.
Quick Answer: What Are the UK Corporation Tax Deadlines and Penalties?
Most companies must pay Corporation Tax 9 months and 1 day after their accounting period ends, and file the Company Tax Return within 12 months of that date.
For returns due on or after 1 April 2026, a late return costs £200 immediately, rising to £400 after three months, plus further charges if it stays outstanding. Interest is charged separately on unpaid tax.
Key points:
- Payment deadline: 9 months and 1 day after the accounting period ends.
- Filing deadline: 12 months after the accounting period ends.
- A return is required even if there is a loss or no tax to pay.
- Late payment attracts daily interest, not usually a fixed penalty.
- Companies House has its own, separate accounts deadline and penalties.
What Is UK Corporation Tax, and Which Rate Applies?
Corporation Tax is the tax a company pays on its taxable profits. Companies and associations that receive a notice to deliver a Company Tax Return must report their profits to HMRC. It is different from Income Tax, which individuals pay. ICT explains the distinction in its guide to corporate tax vs income tax.
Read: Common Mistakes Foreign Entrepreneurs Make in the Netherland
Which Corporation Tax Rate Applies?
For companies with profits over £250,000, the main rate is 25%. Companies with profits between £50,000 and £250,000 pay the main rate reduced by marginal relief, which creates a gradual increase in the effective rate.
A 19% small profits rate applies to companies with profits of £50,000 or less. The limits are reduced where a company has associated companies, so a group of companies should check its position carefully.
Rates are set for each financial year starting on 1 April, so confirm the current figures on GOV.UK before you calculate a bill. For planning ideas once you know your rate, see ICT’s guide to corporate tax planning.
What Is the Difference Between an Accounting Period and a Financial Year?
An accounting period is the period your return covers. It usually follows your company’s own accounts year. HMRC cannot accept a Corporation Tax accounting period longer than 12 months.
The government’s “financial year” is the fixed 1 April to 31 March year that rates are set for. You pay tax at the rates that applied during your company’s accounting period.
The distinction matters because both of your deadlines run from the end of your accounting period, not from 31 March. If you are comparing systems, ICT’s overview of corporate tax in Pakistan shows how Pakistan frames its own tax year.
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