IF MONTH([Order Date]) = MONTH(MAKEDATE(2017, 12, 15))

AND YEAR([Order Date]) = YEAR(MAKEDATE(2017, 12, 15))

AND DAY([Order Date]) <= DAY(MAKEDATE(2017, 12, 15))

THEN [Sales]

END

_______________________________

[TODAY] is a parameter, or can be replaced by the function TODAY()


IF DATEDIFF('year', [Order Date], [Today]) = 0 

AND DATEDIFF('month', [Order Date], [Today]) = 0 

AND [Order Date] <= [Today]

THEN [Sales]

END