Compared to Report Designer version 4.x the logic on how to add period functions has changed. In order to add for example YTD (year to date) function on a column you need to follow the steps below:

1. Drag Period into the report.
2. Add Expaning on the column.
3. Go to Period function

 

4. Drag the Year to date period function into the Filter tab within the Layout Editor (on the column):

If you want aggregated data you can drag the Period function into the Period Aggregation tab.