Corporation Tax UK: A Complete Guide for Finance Professionals 2026

Corporation Tax is the tax companies pay on their profits, and understanding it is essential for accountants, finance professionals and business owners. This guide explains what Corporation Tax is, how it works in the UK, how taxable profits are arrived at, and what companies need to know — in clear, plain language. Because Corporation Tax rates, rules and deadlines change over time, always check the current position with HMRC or a qualified adviser for your specific circumstances. For broader tax study, see our ACCA TX taxation guide.

What is Corporation Tax?

Corporation Tax is a tax on the profits of companies (and some other organisations). UK-resident companies are generally subject to Corporation Tax on their profits, including trading profits, investment income and chargeable gains. Unlike individuals, who pay income tax and capital gains tax, companies bring these together within the Corporation Tax system. A company must work out its taxable profits, calculate the tax due, report it to HMRC, and pay it — all within the relevant deadlines. Corporation Tax is therefore a central, recurring obligation for companies, and getting it right is an important part of running a business correctly and compliantly.

How taxable profits are calculated

A company's Corporation Tax is based on its taxable profits, which are not simply the same as the profit shown in its accounts. The accounting profit is the starting point, but it must be adjusted to arrive at the taxable figure. Common adjustments include:

• Disallowing certain expenses — some costs in the accounts aren't allowable for tax and must be added back.
• Capital allowances — tax relief given for certain capital expenditure, often replacing accounting depreciation (which is itself disallowed).
• Adjusting for different income types — some income may be taxed differently or separately.

The result of these adjustments is the taxable profit on which Corporation Tax is charged. The detailed rules on what's allowable and how adjustments work are complex and change over time, so current guidance should always be checked.

Rates, payment and returns

Corporation Tax is charged at a rate (or rates) set by the government, which can change from year to year, and which may vary depending on the level of profits. Because rates and any profit thresholds change, it's essential to check the current rates rather than relying on a fixed figure. Companies must also file a Corporation Tax return and pay the tax due within set deadlines, which depend on the company's circumstances — larger companies may have different payment arrangements from smaller ones. Meeting these filing and payment deadlines is an important compliance obligation, and missing them can lead to penalties and interest.

Reliefs and allowances

The Corporation Tax system includes various reliefs and allowances that can reduce the tax a company pays. Capital allowances give relief for qualifying capital expenditure; relief is generally available for trading losses, which can often be set against other profits or carried forward or back within the rules; and there are specific reliefs in areas the government chooses to encourage, such as certain research and development activities. The availability and details of these reliefs are set by the rules and change over time, often with specific conditions. Identifying which reliefs a company can use — and applying them correctly — is an important part of managing Corporation Tax, and an area where advice is often valuable.

Why understanding Corporation Tax matters

For companies and their advisers, understanding Corporation Tax matters for both compliance and financial management. Getting it wrong — miscalculating taxable profits, missing deadlines, or overlooking reliefs — can lead to penalties, interest or unnecessary tax. A good understanding helps companies stay compliant, plan effectively, and make sound decisions. Because the rules are detailed and change regularly, this guide is a general overview only. Always check the current rates, rules and deadlines with HMRC, and seek qualified advice for specific situations, rather than relying on general information alone.

Frequently asked questions

What is Corporation Tax?

A tax on the profits of companies (and some other organisations), covering trading profits, investment income and chargeable gains within a single system.

Are taxable profits the same as accounting profits?

No — the accounting profit is the starting point, but it's adjusted (for example, disallowing certain expenses and giving capital allowances) to arrive at the taxable profit.

How are Corporation Tax rates set?

Rates are set by the government and can change from year to year, sometimes varying with the level of profits — so always check the current rates.

What reliefs are available?

Reliefs and allowances such as capital allowances, relief for trading losses, and specific reliefs (for example, for certain R&D) can reduce the tax due, subject to current rules and conditions.

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