Impurities are not acceptable in drug formulation. It is considered as unwanted chemicals or organic material which remains with active pharmaceutical ingredient (APIS). The impurity is produced either during formulation or ageing of both APIs and finished dosage form. The existence of these undesired chemicals may influence the safety and the efficacy of the pharmaceutical finished products. In this review article we have discussed about the methodologies adopted by United States of Europe for impurity profiling given by their respective regulatory authorities. Impurity profiling, calculation, and methodologies used to represent impurities in dosage regulation related documents.