Aspects of the present disclosure address systems and methods for functional coverage in integrated circuit (IC) designs utilizing arbitrary expression to define irrelevant domains in coverage item definitions. A coverage item definition is determined to include an arbitrary expression that defines an irrelevant domain for a coverage item in a functional coverage analysis of an IC design. Based on determining if the item definition comprises the arbitrary expression, a verification the arbitrary expression satisfies one or more analyzability conditions is performed. Based on verifying the arbitrary expression satisfies the one or more analyzability conditions, the irrelevant domain for the coverage item is calculated based on the arbitrary expression. An enhanced functional coverage model that excludes the irrelevant domain for the coverage item is generated and used to perform the functional coverage analysis on the IC design.