Corporation Tax Calculator

Corporation Tax (CT) is the tax UK limited companies pay on their taxable profits — trading profits, investment income, and chargeable gains, after deducting allowable expenses, capital allowances, and any reliefs. For 2025/26 the headline structure is unchanged from 2024/25: 25% main rate on profits over £250,000, 19% small profits rate for profits up to £50,000, and a marginal relief sliding scale producing effective rates between 19% and 25% on profits between £50,000 and £250,000. This calculator handles the marginal relief calculation precisely. The standard fraction for 2025/26 is 3/200 (giving a 26.5% marginal rate of tax on profits in the £50,000-£250,000 band — yes, higher than 25%, because every pound in this band withdraws a slice of the small profits benefit). For a profit of £100,000 the effective rate is approximately 23.5%; for £200,000 it is approximately 24.65%. The thresholds reduce proportionally if the company has associated companies (under common control) — two associates share £25,000/£125,000 each, dragging more companies into the 25% main rate. Corporation Tax is UK-wide — there is no devolution. Welsh, Scottish and Northern Irish companies follow the same rates (though Northern Ireland has historically explored devolved CT). Payment is due 9 months and 1 day after the accounting period end for companies under £1.5m profits; larger companies pay quarterly instalments. The CT600 return is due 12 months after period end, although in practice most companies file at the same time as paying. Key reliefs reduce the bill: the Annual Investment Allowance gives 100% relief on the first £1m of qualifying plant and machinery; full expensing makes that permanent for new equipment from April 2026; R&D tax relief (now mostly the merged RDEC at 20% above the line — net benefit ~15-16%, see our R&D calculator); Patent Box at 10% on profits from patented inventions; group relief on losses between 75%-owned group companies. The calculator does not model these reliefs in detail — input your taxable profit AFTER reliefs to get the right CT figure. Dividends paid to shareholders are not deductible (they come out of post-tax profit), but director salaries and pension contributions are — the basis of most owner-managed-company tax planning.