Moyenne mobile

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 )

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