Associated company rules: Protecting your corporation tax thresholds

Running more than one limited company is common for many owner-managers, but corporation tax rules may treat those companies as connected. This guide explains how associated company rules apply for accounting periods within the corporation tax financial year starting 1 April 2026, how thresholds for the 19% small profits rate, 25% main rate and marginal relief can be divided between companies, and the practical steps that can help protect your position.