There are five corporate interest restriction action deadlines with a 31 March 2018 date. Those affected by the rules will need to get to grips with a range of new definitions and concepts. Some thought should be given to planning how to do the calculations and how to meet the various reporting obligations. Consideration will need to be given to both time apportionment and just and reasonable apportionment bases for apportioning results of periods of account straddling the 1 April 2017 commencement date.