Corporation Tax Knowledge Base

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.

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.

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.

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 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.

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 & 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 33.75% 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.

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.

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.

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.

CT Rates History

Current and historical Corporation Tax rates since 2010.

Key Corporation Tax Dates

Every important CT deadline mapped to your accounting period.

Corporation Tax Glossary

Plain-English definitions of common Corporation Tax terms and acronyms.