The paper deals with microsimulation - an increasingly popular instrument used for policy analysis, especially in the field of individual and corporate income taxation. The aim of the paper is twofold. First, it discusses some key aspects of microsimulation with a particular focus on its types and implementations in tax policy research. Secondly, it presents a microsimulation analysis of the effects of unlimited inter-period loss offset in corporate income tax. The investigation is based on a panel of 222 corporations active in Poland, which was derived from the InfoCredit database. The microsimulation is carried out in a multi-period setting (2007-2012). It considers a perspective of taxpayers with a particular focus on individual tax burden and distributional effects of taxation. The analysis shows that the expected overall consequences of the tax reform in question would be rather moderate, however the size of the effects would vary strongly across firms.