Corporation tax Corporation tax rates are set for each Financial Year. A Financial Year runs from 1 April to the following 31 March.If the accounting period of a company straddles the 31 March, the profits are apportioned on a time basis to each Financial Year.The Northern Ireland Executive has committed to setting the rate of corporation tax at 12.5% when the Northern Ireland Executive demonstrates its finances are on a sustainable footing.Year to 31.3.25: Rate Profits band (£) Rate (%) Small profits rate 0 - 50,000 19 Marginal rate 50,001 - 250,000 26.5 Main rate Over 250,000 25 Marginal relief fraction 3/200