Business cycles demonstrate economic activity in economy. Synchronization of business cycles of EU member states is crucial, precisely because the separation of monetary sovereignty would bring minimal costs to the domestic economy. This paper analyzes the synchronization of business cycles within the European Union, which, according to the theory of the optimal currency area is considered one of the most important criteria for the successful implementation of the common monetary policy. Three methods were used to determine the level of business cycle compliance: concordance index, cross-correlation, and rolling cross-correlation. The synchronization analysis was conducted based on quarterly data on real GDP of all EU Member States and the EU27 as an aggregate area. The analysis covers the period from the first quarter of 1995 (1995Q1) to the first quarter of 2021 (2021Q1), while the concordance index and cross-correlation were calculated for two subperiods, 1995Q1 – 2008Q1 and 2008Q1 – 2021Q1, in order to observe changes in compliance. Based on the results obtained from the concordance index and cross-correlation, it can be concluded that the cycles of all Member States are synchronized with the European Union cycle. New Member States in general are less synchronized while the old Member States are highly synchronized. Additionally, the results show that a higher level of compliance was achieved in the second subperiod. The results of the rolling cross-correlation imply that the common monetary policy is most appropriate for the old Member States and for the Czech Republic, Cyprus, Poland and Slovenia from the group of new Member States since their compliance with the EU cycle is high and stable throughout the period.