It is preferential to do it as part of a calendar table, implemented in the Universe.
If you want a quicker/dirtier Webi approach, use this:
=If(MonthNumberOfYear([Date Object])<4;FormatNumber(Year([Date Object])-1;"0")+"-"+FormatNumber(Year([Date Object]);"0");FormatNumber(Year([Date Object]);"0")+"-"+FormatNumber(Year([Date Object])+1;"0"))
As you can see, it's quite complex, hence the recommendation to use a proper calendar table.