Corporation Tax marginal relief and associated companies calculator

Use this Corporation Tax calculator to estimate your limited company’s tax liability, including Marginal Relief and adjustments for associated companies.

The calculator also allows for relevant exempt distributions when calculating augmented profits.

Based on the Corporation Tax rates and thresholds applying in 2026/27.

Marginal Relief and Associated Companies Corporation Tax Calculator

Notes and assumptions

Corporation Tax rates and thresholds

The current Corporation Tax system has two main rates.

For a standard company with a 12-month accounting period and no associated companies, profits of £50,000 or less are generally charged at the 19% small profits rate.

Profits above £250,000 are generally charged at the 25% main rate.

Where profits fall between these limits, Marginal Relief gradually increases the effective Corporation Tax rate from 19% towards 25%.

HMRC – Corporation Tax rates and allowances

You can also use the government’s official Marginal Relief calculator to compare the results.

How Marginal Relief is calculated

Where a company falls within the Marginal Relief range, Corporation Tax is initially calculated using the 25% main rate and then reduced by Marginal Relief.

The standard Marginal Relief fraction is 3/200.

Where augmented profits differ from taxable profits, the calculator uses the full Marginal Relief formula:

Marginal Relief = 3/200 × (adjusted upper limit − augmented profits) × taxable profits ÷ augmented profits

Corporation Tax due is then:

(taxable profits × 25%) − Marginal Relief

If the company has no relevant exempt distributions, augmented profits and taxable profits will normally be the same and the calculation becomes simpler.

HMRC Company Taxation Manual – Marginal Relief

Associated companies

If your company has any associated companies, the £50,000 and £250,000 profit limits are divided by the total number of associated companies, including your own company.

For example, if your company has one other associated company, there are two companies in total and the limits are reduced to £25,000 and £125,000 for each company.

If there are two other associated companies, making three companies in total, the limits are divided by three.

The calculator asks you to enter the number of other associated companies and automatically adjusts both Corporation Tax limits.

HMRC – Associated companies and Corporation Tax

Taxable profits and augmented profits

Marginal Relief can depend on both your company’s taxable profits and its augmented profits.

Augmented profits broadly consist of taxable total profits plus relevant exempt distributions received by the company.

For many small trading companies there will be no relevant exempt distributions, in which case you can leave this field at £0.

If relevant exempt distributions are entered, the calculator adds them to taxable profits when determining whether the company falls within the small profits, Marginal Relief or main-rate range, and when calculating Marginal Relief.

HMRC Company Taxation Manual – Augmented profits

Accounting periods and other limitations

The calculator assumes a 12-month accounting period.

If your Corporation Tax accounting period is shorter than 12 months, the £50,000 and £250,000 limits must normally be reduced proportionately. This calculator does not make that adjustment automatically.

It also does not cover specialist Corporation Tax regimes or every possible tax adjustment, relief or company structure.

If your company has a short accounting period, complex investment income, unusual arrangements or other Corporation Tax complications, you should confirm the calculation with HMRC or speak to a qualified accountant.