UK Corporation Tax 25% Rates & Marginal Relief Guide 2026

Authoritative tax guide for UK limited companies: statutory Corporation Tax rates (19% Small Profits Rate vs 25% Main Rate), Marginal Relief sliding scale calculation (£50,000 to £250,000 thresholds), and HMRC CT600 payment deadlines.

1. 19% Small Profits Rate vs 25% Main Rate Banding

UK Limited Companies pay Corporation Tax on taxable profits generated during each accounting period. Under statutory rules, tax rates are determined by profit thresholds:

Taxable Profit Threshold Band	Statutory Corporation Tax Rate	Relief / Calculation Formula
Profits up to £50,000	19% Small Profits Rate	Standard 19% flat rate tax
Profits between £50,001 and £250,000	Marginal Rate (Tapered 19% to 25%)	25% Main Rate MINUS Marginal Relief Fraction (3/200)
Profits exceeding £250,000	25% Main Rate	Standard 25% flat rate tax

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2. CT600 Filing Deadlines & Associated Companies Rule

• Payment Deadline: For a company that is not required to pay Corporation Tax by quarterly instalments, Corporation Tax is normally due **9 months and 1 day** after the end of the accounting period. Companies within the quarterly-instalment regime have different payment dates. • Return Deadline: The Company Tax Return (CT600) must normally be filed within **12 months** of the end of the accounting period. • Marginal Relief: For a standard 12-month accounting period with no associated companies, the lower limit is £50,000 and the upper limit is £250,000. The standard Marginal Relief fraction is **3/200**, not 3/400. • Associated Companies Rule: The £50,000 and £250,000 limits are proportionately reduced where a company has associated companies. The divisor is based on the number of associated companies plus the company itself. • Short Accounting Periods: The lower and upper limits are also reduced proportionately where the accounting period is shorter than 12 months.

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Key Takeaways

Marginal Relief applies between the £50,000 and £250,000 limits for a standard 12-month accounting period, subject to the associated-company and short-period rules.
The standard Marginal Relief fraction for non-ring-fence profits is 3/200.
Corporation Tax is normally due 9 months and 1 day after the accounting period ends unless quarterly instalment rules apply.
The CT600 is normally due within 12 months of the accounting period end.
Associated companies and short accounting periods can reduce the £50,000 and £250,000 limits proportionately.

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Frequently Asked Questions (6 Interlinked FAQs)

For non-ring-fence profits, the small profits rate is 19% where profits are £50,000 or less, while the main rate is 25% where profits exceed £250,000. Profits between those limits may qualify for Marginal Relief.

The standard Marginal Relief fraction is 3/200 for non-ring-fence profits. The relief reduces the 25% main-rate liability for companies whose profits fall between the applicable lower and upper limits.

For companies outside the quarterly-instalment regime, Corporation Tax is normally due 9 months and 1 day after the end of the accounting period. Large companies subject to quarterly instalments have different payment dates.

The Company Tax Return is normally due within 12 months after the end of the accounting period, even though the Corporation Tax payment is usually due earlier.

The limits are reduced proportionately where a company has associated companies. For example, with one associated company, the standard limits are divided by two, subject to the detailed statutory rules.

Yes, qualifying revenue expenses incurred wholly and exclusively for the purposes of the trade can generally reduce taxable profits. The precise tax treatment depends on the type of expenditure and the applicable Corporation Tax rules.