Dynamic Previous Year Sales

Hi All

how can i create a dynamic previous year sales

E.g if i select 2015, i need to retrieve 2014 sales, if i select 2014, i need to retrieve 2013 sales. Also note my financial year ends on 31st March. 

I have tried with below DAX Function , but it didnt not work

1. 

PreviousYearbySelection

 VAR CurrentYear=

CALCULATE(FIRSTNONBLANK('Z_Power BI Date Template'[Year], ISFILTERED('Z_Power BI Date Template'[FinancialYear]) ))
Return
CurrentYear-1

2.Sales_Previous_Year_Selection =

CALCULATE

(sum

('Sales Comparison'[BaseSubTotal]),

filter ('Z_Power BI  Date Template','Z_Power BI  Date Template'[Year]=[PreviousYearbySelection]

)

)