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UK Corporation Tax is the tax paid by limited companies on their taxable profits. From April 2023, the UK operates a dual-rate system: a small profits rate of 19% applies to companies with profits up to £50,000, while the main rate of 25% applies to companies with profits above £250,000. Between £50,000 and £250,000 there is a marginal relief calculation that gradually increases the effective rate from 19% to 25%. Companies with associated companies must divide the £50,000 and £250,000 thresholds equally between all associated entities, which significantly reduces the limits for groups. The Annual Investment Allowance (AIA) allows up to £1 million of qualifying plant and machinery expenditure to be deducted fully in the year of purchase. The Research and Development (R&D) expenditure credit scheme for large companies (RDEC) provides an above-line credit of 20% on qualifying R&D costs. The merged SME and RDEC scheme took effect from April 2024. The Patent Box regime taxes profits from patented inventions at a special rate of 10%. Corporation tax returns are filed nine months after the accounting period end, with payment due nine months and one day after the year end (for non-large companies).
Marginal relief: Tax = Main rate × profits - Marginal Relief Fraction × (Upper limit - profits) × profits / total profits; MRF = 3/200
- 1Determine the company's taxable profits for the accounting period (after allowable expenses, capital allowances, and any loss reliefs)
- 2Check whether the company has associated companies — if so, divide the £50,000 and £250,000 thresholds by the number of associated companies plus one
- 3If profits are £50,000 or below: tax = profits × 19%
- 4If profits exceed £250,000: tax = profits × 25%
- 5If profits are between £50,000 and £250,000: apply the marginal relief formula: tax = (profits × 25%) - ((250,000 - profits) × profits / total profits × 3/200)
- 6Deduct any R&D tax credits, Patent Box relief, or other reliefs from the corporation tax liability
- 7File the CT600 return and pay the tax nine months and one day after the end of the accounting period (for small and medium companies)
Profit ≤ £50,000 small profits rate applies. £40,000 × 19% = £7,600.
A solo company with £40,000 profit falls within the small profits rate band and pays 19% corporation tax with no marginal relief calculation required.
Marginal relief: (£150,000 × 25%) - (3/200 × (£250,000 - £150,000) × 1) = £37,500 - £1,500 = £36,000. Effective rate = 24%.
Profits in the marginal relief band attract a blended rate between 19% and 25%. The marginal relief fraction reduces the headline 25% tax by a declining amount as profits approach £250,000.
Profit exceeds £250,000 upper limit. Flat 25% applies.
Once profits exceed £250,000 (or the divided threshold for groups), the flat 25% main rate applies with no marginal relief reduction.
With 3 associated companies, thresholds are divided by 4. The £80,000 profit now exceeds the adjusted upper limit of £62,500, so the full 25% main rate applies instead of the beneficial rates.
Limited company owners calculating their annual corporation tax liability, representing an important application area for the Uk Corporation Tax in professional and analytical contexts where accurate uk corporation tax calculations directly support informed decision-making, strategic planning, and performance optimization
Accountants preparing CT600 returns and tax computations for clients, representing an important application area for the Uk Corporation Tax in professional and analytical contexts where accurate uk corporation tax calculations directly support informed decision-making, strategic planning, and performance optimization
Business owners deciding whether to accelerate capital expenditure to use AIA in the current year, representing an important application area for the Uk Corporation Tax in professional and analytical contexts where accurate uk corporation tax calculations directly support informed decision-making, strategic planning, and performance optimization
R&D-intensive businesses calculating their RDEC credit to reduce the effective tax rate, representing an important application area for the Uk Corporation Tax in professional and analytical contexts where accurate uk corporation tax calculations directly support informed decision-making, strategic planning, and performance optimization
Group companies planning loss surrender between members to minimise group-wide tax, representing an important application area for the Uk Corporation Tax in professional and analytical contexts where accurate uk corporation tax calculations directly support informed decision-making, strategic planning, and performance optimization
Close Company Loans to Participators
{'title': 'Close Company Loans to Participators', 'body': 'If a close company (broadly, a company controlled by 5 or fewer shareholders) makes a loan to a participator (shareholder) that is outstanding 9 months after year end, the company pays a temporary corporation tax charge of 33.75% on the loan amount. This is repaid when the loan is repaid.'}
Dormant Companies
In the Uk Corporation Tax, this scenario requires additional caution when interpreting uk corporation tax results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when uk corporation tax calculations fall into non-standard territory.
Group Relief
In the Uk Corporation Tax, this scenario requires additional caution when interpreting uk corporation tax results. The standard formula may not fully account for all factors present in this edge case, and supplementary analysis or expert consultation may be warranted. Professional best practice involves documenting assumptions, running sensitivity analyses, and cross-referencing results with alternative methods when uk corporation tax calculations fall into non-standard territory.
Extremely large or small input values in the Uk Corporation Tax may push uk
Extremely large or small input values in the Uk Corporation Tax may push uk corporation tax calculations beyond typical operating ranges. While mathematically valid, results from extreme inputs may not reflect realistic uk corporation tax scenarios and should be interpreted cautiously. In professional uk corporation tax settings, extreme values often indicate measurement errors, unusual conditions, or edge cases meriting additional analysis. Use sensitivity analysis to understand how results change across plausible input ranges rather than relying on single extreme-case calculations.
| Profits Band | Rate | Effective Rate |
|---|---|---|
| Up to £50,000 | 19% (small profits rate) | 19% |
| £50,001 - £250,000 | 25% less marginal relief | 19%-25% (graduated) |
| Above £250,000 | 25% (main rate) | 25% |
| Marginal Relief Fraction | 3/200 | — |
| AIA limit | £1,000,000 p.a. | — |
| RDEC credit rate | 20% | — |
| Patent Box rate | 10% | — |
What is the UK corporation tax rate for small companies?
19% for taxable profits up to £50,000 (or a lower threshold if the company has associated companies). This is the 'small profits rate' introduced from April 2023. This is particularly important in the context of uk corporation tax calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise uk corporation tax computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is marginal relief for corporation tax?
Marginal relief is a mechanism that gradually increases the effective tax rate from 19% to 25% for companies with profits between £50,000 and £250,000. Without it, companies just below £250,001 would face an immediate jump from 19% to 25%. This is particularly important in the context of uk corporation tax calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise uk corporation tax computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What counts as an associated company?
Associated companies are companies under common control (broadly, where one company controls another or both are under common control of a third party). They cause the profit thresholds to be divided, potentially pushing otherwise qualifying companies into higher rate bands. This is particularly important in the context of uk corporation tax calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise uk corporation tax computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
When must corporation tax be paid?
For most companies (non-large): 9 months and 1 day after the end of the accounting period. Large companies with profits exceeding £1.5 million pay in quarterly instalments during the year. This is particularly important in the context of uk corporation tax calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise uk corporation tax computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is the Annual Investment Allowance (AIA)?
The AIA allows 100% first-year deduction of qualifying plant and machinery expenditure up to £1 million per year. This means companies can fully deduct large capital investments immediately rather than over many years via writing-down allowances. This is particularly important in the context of uk corporation tax calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise uk corporation tax computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
How does R&D tax relief work from April 2024?
From April 2024, a merged scheme replaced the previous SME and RDEC schemes. The merged scheme provides a 20% above-the-line RDEC credit on qualifying R&D expenditure, regardless of company size (with a separate intensive rate for loss-making R&D-intensive SMEs). This is particularly important in the context of uk corporation tax calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise uk corporation tax computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is Patent Box?
Patent Box is an optional regime allowing companies to elect to have profits attributable to qualifying patents taxed at 10% rather than the standard 19% or 25%. The company must hold or be exclusively licensed to exploit the relevant patents. This is particularly important in the context of uk corporation tax calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise uk corporation tax computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
Can I carry forward losses from one accounting period to another?
Yes. Trading losses can be carried forward indefinitely (post-April 2017 losses) to offset against future trading profits of the same trade. They can also be carried back one year or surrendered to group members. This is particularly important in the context of uk corporation tax calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise uk corporation tax computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
Pro Tip
If your company's profits are just above £50,000 or £250,000, consider whether delaying income or accelerating deductible expenses into the current period would bring profits into a lower tax band. The difference between 19% and 25% on profits in the marginal relief band is worth careful planning.
Did you know?
UK corporation tax has fallen dramatically over recent decades — it stood at 52% in 1979, then 33% in the 1990s, and reached a record low of 17% before being raised to 25% in 2023. The current two-tier system is a novel approach designed to protect small businesses while raising revenue from larger companies.
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