The article discusses how data on economic activity in Croatia is adjusted for seasonal variations. The Croatian National Bank and the Croatian Bureau of Statistics work together on this process. They identify effects like working days, leap years, and Easter that can impact the data. The article explains the steps taken to adjust the data and the limitations of the models used. Key findings include the identification of working-day effects on all indicators, leap year effects on most indicators, and an Easter effect on retail trade turnover. This information helps users better understand the data and use it for further analysis.