Corporation Tax Knowledge Base
Practical, plain-English guides to UK Corporation Tax — from registering your company to filing your CT600, capital allowances, R&D relief, and more. Every article references official HMRC and GOV.UK sources.
Your complete guide to Corporation Tax — 58 articles covering everything from company registration to capital allowances and R&D relief.
Corporation Tax Fundamentals
What Is Corporation Tax?
The basics: what CT is, who pays it, and how it differs from Income Tax.
Who Pays Corporation Tax?
Limited companies, LLPs, CICs, clubs — and who is exempt.
Corporation Tax Rates
Current rates, the small profits rate, and how marginal relief works.
Accounting Periods
How your company’s financial year maps to its CT accounting period.
Close Companies
What makes a company “close” and the special tax rules that apply.
Setting Up a Company & Tax
Tax essentials when incorporating: Companies House, CT41G, and first-year obligations.
Registration & Filing
Registering for Corporation Tax
How to notify HMRC, the CT41G form, and registration deadlines.
The CT600 Tax Return
What the CT600 covers, key boxes, and how to file it.
Filing Deadlines
When accounts and CT600 returns are due — and what happens if you miss them.
Amending a CT600
How to correct mistakes on your Company Tax Return within the time limit.
Filing a Long Accounting Period
Two CT600s, one set of accounts, and box 85 — including long first periods.
iXBRL & Digital Filing
What iXBRL tagging is, why it’s required, and how to file digitally.
Company Accounts Requirements
Statutory accounts, micro-entities, FRS 102/105, and filing obligations.
Calculating Taxable Profits
Taxable Profits Explained
How accounting profit becomes taxable profit: adjustments, add-backs, and deductions.
Allowable Business Expenses
What you can deduct: the “wholly and exclusively” rule for companies.
Disallowable Expenses
Common expenses you must add back: entertaining, depreciation, fines, and more.
Trading Income for Companies
How HMRC determines whether your company is “trading” and how profits are calculated.
Non-Trading Income
Investment income, property rental, and other non-trading receipts.
Loan Relationships
How companies account for interest, borrowing costs, and corporate bonds.
Chargeable Gains for Companies
How capital gains work for companies: indexation, SSE, and BADR.
Capital Allowances
Capital Allowances Overview
How capital allowances replace depreciation for tax purposes.
Annual Investment Allowance (AIA)
100% relief on up to £1 million of qualifying plant and machinery.
Full Expensing
Permanent 100% first-year allowance for qualifying new plant and machinery.
Writing Down Allowances
The 18% and 6% reducing balance allowances for the main and special rate pools.
Structures & Buildings Allowance
3% annual relief on construction and renovation of commercial buildings.
Balancing Charges & Disposals
What happens to your capital allowance pools when you sell or dispose of assets.
Corporation Tax Reliefs
R&D Tax Relief
Enhanced deductions and tax credits for companies investing in research and development.
The Merged R&D Scheme
The new unified R&D regime from April 2024: rates, rules, and how to claim.
Creative Industry Tax Reliefs
Reliefs for film, TV, animation, video games, theatre, and orchestras.
Patent Box
A reduced 10% effective CT rate on profits from patented inventions.
Trading Losses
Carry back, carry forward, and group relief options for company losses.
Marginal Relief
How companies with profits between £50,000 and £250,000 pay an effective rate below 25%.
Dividends & Directors
Dividends & Corporation Tax
How dividends received and paid are treated for CT purposes.
Directors’ Loan Accounts
How the director’s loan account works: overdrawn balances, repayments, and bed & breakfasting.
Section 455 Tax
The 35.75% tax charge on loans to participators — and how to reclaim it.
Benefits in Kind for Directors
Company cars, medical insurance, and other taxable benefits — the CT and NIC implications.
Salary vs Dividends
The most tax-efficient way to extract profits as a director-shareholder.
Payments & Penalties
Paying Corporation Tax
All payment methods, your CIPP reference, and how to set up payments.
Payment Deadlines
The 9-months-and-1-day rule and when your CT bill is actually due.
Quarterly Instalment Payments
When large and very large companies must pay CT in advance quarterly instalments.
Interest & Penalties
Late filing penalties, late payment interest, and how to avoid them.
Corporation Tax Refunds
How to claim a refund for overpaid CT, including loss carry-back claims.
Groups & Associated Companies
Associated Companies
How associated companies affect your CT rate thresholds.
Group Relief
Surrendering trading losses between group companies.
Capital Gains Group Relief
No gain/no loss transfers between group members and degrouping charges.
Transfer Pricing
The arm’s length principle for transactions between connected parties.
Substantial Shareholding Exemption
Tax-free disposal of subsidiary shares under the SSE rules.
Special Situations
Dormant Companies
Obligations for dormant companies with HMRC and Companies House.
Non-UK Companies & CT
When overseas companies are liable to UK Corporation Tax.
Striking Off & Dissolution
How to close your company: DS01, ESC C16, and capital distribution treatment.
Members’ Voluntary Liquidation
Formal liquidation to extract retained profits as a capital distribution.
CT for Charities & CICs
Exemptions and reliefs available to charities and community interest companies.
Annual Tax on Enveloped Dwellings
The annual charge on companies holding UK residential property worth over £500,000.
Questions?
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