Sales R12M =
VAR NumOfMonths = 12
VAR LastCurrentDate =
MAX ( 'Date'[Date] )
VAR Period =
DATESINPERIOD ( 'Date'[Date], LastCurrentDate, - NumOfMonths, MONTH )
VAR Result =
CALCULATE (
AVERAGEX (
VALUES ( 'Date'[Calendar Year Month] ),
[Sales Amount]
),
Period
)
VAR FirstDateInPeriod = MINX ( Period, 'Date'[Date] )
VAR LastDateWithSales = MAX ( Sales[Order Date] )
RETURN
IF ( FirstDateInPeriod <= LastDateWithSales, Result )