Corporation Tax Explained

How UK companies calculate taxable profit, apply Corporation Tax rates and meet filing deadlines.

Reviewed against official HMRC guidance

Tax year
2026/27
Last reviewed
August 2026
Reading time
10 min

Who pays Corporation Tax

Who this guide is for: For limited company owners who need to understand taxable company profit, rates and deadlines — before modelling personal extraction.

UK limited companies pay Corporation Tax on taxable profits for each accounting period. It is a company liability, not a PAYE deduction from directors' salaries.

  1. Step 1Company profit
  2. Step 2Salary & employer costs

    Separate company cost branches

    • Branch AEmployer National Insurance
    • Branch BEmployer pension
  3. Step 3Corporation Tax (highlighted in this guide)
  4. Step 4Post-tax reserves
  5. Step 5Dividends
  6. Step 6Personal tax
  7. Step 7Take-home cash

Employer National Insurance and employer pension contributions usually reduce taxable company profit before Corporation Tax. Dividends come later, from post-tax distributable reserves, and personal tax is calculated on what the director receives.

Corporation Tax sits after deductible remuneration costs and before dividend capacity.

How taxable company profit is built

Start from trading profit (and other chargeable profits), then adjust for items such as:

  • Director or employee salary (usually deductible)
  • Employer National Insurance on that pay
  • Employer pension contributions where they meet the deductibility rules — see Employer Pension Contributions Explained
  • Disallowable expenses added back
  • Capital allowances instead of accounting depreciation

Rates in Northline's 2026/27 director overlay

Corporation Tax structure from the FY2026 director overlay. Limits shown are the unadjusted full-year figures.
BandTaxable / augmented profitsRate
Small profits rateUp to £50,000.0019%
Marginal relief£50,000.00 to £250,000.00Between 19% and 25%
Main rateOver £250,000.0025%

Associated companies

Broadly, companies can be associated where the same person or persons control them, and commercial interdependence can also matter. The legal test is detailed — treat the notes below as a planning overview, not a full legal assessment.

For the rate limits, the divisor is the number of associated companies including the company itself — that is, other associated companies plus one.

How other associated companies change the full-year limits in Northline's adjustProfitLimit helper.
Other associated companiesDivisorLower limitUpper limit
01£50,000.00£250,000.00
12£25,000.00£125,000.00
34£12,500.00£62,500.00

Augmented profits are taxable total profits plus certain exempt distributions received. Rate banding uses augmented profits; the tax itself is charged on taxable profits (with marginal relief calculated from the rules above).

Three different clocks

Data table
ClockWhat it is
Personal tax year6 April to 5 April (for example 2026/27) — used for Income Tax and Dividend Tax.
Company accounting periodThe period the company prepares accounts for — often 12 months, but can be shorter.
Corporation Tax financial year1 April to 31 March. Accounting periods that span financial years may need careful rate treatment.

Worked marginal relief example

£100,000.00 taxable profit — marginal relief

Financial year FY2026 · England · 0 other associated companies · 12-month accounting period · no exempt distributions. Figures from the shared Corporation Tax engine.

£100,000.00 taxable profit — marginal relief
Taxable profit£100,000.00
Lower profit limit (adjusted)£50,000.00
Upper profit limit (adjusted)£250,000.00
RegimeMarginal relief
Headline rate before relief25%
Marginal relief£2,250.00
Corporation Tax due (key figure)£22,750.00
Effective rate (key figure)22.75%

If the accounting period straddles a financial-year rate change, Northline may simplify the period — check the calculator warnings for your inputs.

Calculate your Corporation Tax with associated companies and your accounting period Use the Corporation Tax Calculator

Payment and filing deadlines

  • Corporation Tax payment — for most companies, nine months and one day after the end of the accounting period. Large companies may pay by instalments.
  • Company tax return — normally due 12 months after the end of the accounting period.

Shorter or longer accounting periods change the date arithmetic. Always confirm due dates for your company on GOV.UK.

Where to go next

Frequently asked questions

Are dividends deductible?

No. Dividends are not a company expense and do not reduce taxable profits for Corporation Tax. Salary, employer National Insurance and allowable employer pension contributions usually can.

How do associated companies affect the limits?

The lower and upper profit limits are divided by the number of associated companies including the company itself. With no other associated companies the full £50,000.00 / £250,000.00 limits apply for a 12-month period. With one other associated company those limits are typically halved.

What happens if the accounting period is shorter than 12 months?

The profit limits are usually time-apportioned for periods shorter than 12 months, as well as being divided for associated companies. Do not assume the full-year limits always apply unchanged.

When is Corporation Tax due?

For most companies, Corporation Tax is payable nine months and one day after the end of the accounting period. The company tax return is normally due 12 months after the end of the accounting period. Large companies can have different instalment rules — check GOV.UK for your company.

Official sources

Related calculators

Related guides

Next steps

This guide is for general information only. It is not tax, legal or financial advice. Always check the official guidance for your situation.