UK Corporation Tax Calculator (2026/27).

Companies with taxable profits up to £50,000 pay the small-profits rate of 19%. Above £250,000 the main rate of 25% applies. Between these thresholds the company is in the marginal-relief band — it pays 25% but receives a sliding-scale rebate using HMRC's 3/200 marginal-relief fraction.

Marginal relief is calculated as 3/200 × (£250,000 − augmented profits). This produces an effective tax rate between 19% and 26.5% as profits rise through the band. The calculator above shows the gross 25% charge and the marginal relief deduction separately.

Two companies are associated if one controls the other, or both are controlled by the same person or group of people. Associated companies share the £50,000 and £250,000 thresholds equally, which can push your company into the higher band sooner. The rules tightened from 1 April 2023 — Countify can review your group structure to confirm exposure.

Yes — Corporation Tax rates apply by financial year (FY) running 1 April to 31 March. An accounting period that straddles two financial years is apportioned. For an April-to-March year-end, FY 2026 covers the whole period and the rates above apply throughout.

The CT600 return is due 12 months after the end of the accounting period. The Corporation Tax payment is due earlier — 9 months and 1 day after the period end (or in quarterly instalments for very large companies). Use our deadline checker to confirm your exposure.