Definition
Corporation Tax is the tax UK limited companies pay to HM Revenue and Customs (HMRC) on their taxable profits. The rates, unchanged since 1 April 2023 and still in place for the year from 1 April 2026, are 19% on profits of £50,000 or less and 25% on profits over £250,000, with Marginal Relief in between. HMRC does not send a bill: the company works out the tax, reports it on the CT600 and pays it.
Two separate deadlines
| Step | Deadline |
|---|---|
| Pay Corporation Tax | 9 months and 1 day after the accounting period ends |
| File the CT600 | 12 months after the accounting period ends |
For an accounting period ending 31 December 2026, the tax is due by 1 October 2027 and the return by 31 December 2027. Late payment carries interest at the Bank of England base rate plus 4%.
What is taxed
The tax is charged on taxable total profits: trading profits, investment income and chargeable gains after tax adjustments, allowances and reliefs. The profit in the accounts is only the starting point. A company with no associated companies and £40,000 of taxable profit in a 12-month period pays £7,600; at £100,000 it pays £22,750 after Marginal Relief. For other profit levels, see Corporation Tax rates for 2026/27.
SmartFiling’s Corporation Tax filing service prepares the computation and files the CT600.
Related questions
- When is Corporation Tax due? Usually 9 months and 1 day after the accounting period ends.
- Is filing the CT600 the same as paying Corporation Tax? No. They are separate steps with separate deadlines.
Related terms
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CT600
The CT600 is the Company Tax Return a UK company files with HM Revenue and Customs (HMRC) for each accounting period.
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Accounting period
An accounting period is the period covered by a company's Company Tax Return (CT600) and used to calculate its Corporation Tax.
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Small profits rate
The small profits rate is the 19% rate of Corporation Tax for companies with profits of £50,000 or less in a 12-month accounting period.
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Marginal Relief
Marginal Relief is a reduction in Corporation Tax for companies with profits between £50,000 and £250,000.
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Taxable total profits
Taxable total profits are the profits on which a UK company pays Corporation Tax for an accounting period.
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