When Things Get Weird with Custom Calendars in Tabular Models

# When Custom Calendars in Business Analytics Go Wrong If you use Power BI or Microsoft Fabric to analyze your business data, a newer feature lets you set up custom calendars to match your company's unique fiscal year or reporting periods—but it can create unexpected problems if not set up carefully. The feature has only been available since September 2025, so many teams are still learning where things can go wrong. Understanding these pitfalls before you implement a custom calendar can save you from discovering errors in your reports later.