Current and Prior Period Measures

DAX DAX Calculations
8

Sorry I got confused. The original formula is correct, there was no need to change it.

It look like all you need to do actually is adjust the below

Prior Quarter Sales = 
VAR CurrentQuarter = LOOKUPVALUE( Dates[QuarterOfYear], Dates[Date], TODAY() )
VAR CurrentYear = YEAR( TODAY() )

RETURN
CALCULATE( [Total Sales],
    FILTER( ALL( Dates ),
        IF( CurrentQuarter = 1,
        Dates[Year] = CurrentYear - 1 && Dates[QuarterOfYear] = 4,
        Dates[Year] = CurrentYear && Dates[QuarterOfYear] = CurrentQuarter - 1 ) ) )

Just make sure to add the minus 1 to the end of the formula.