Time Intelligence Functions in DAX
One of the most common calculations performed in data analysis is to compare some number to a comparable number for a different time period. Calculations that make comparisons to last month or to the same period from a year ago are very important for any business intelligence tool. Toward that end, DAX introduces 35 new functions expressly for the purpose of working with time based data.
Concepts and Best Practices
Whenever you are defining measures and working with time periods, there are many opportunities to make bad assumptions about what the PivotTable in which the measure will be used might look like. To avoid a lot of those problems, DAX makes certain assumptions and we recommend certain best practices for anyone planning to use the time intelligence functions described here.