DAX Calculate, in this case, orders placed and sent same period, month

I have attached a simple table showing what I'd like to achieve but without using the calculated column,

essentially, I just used and if statement and then summed the result in a measure,

 IF(	MONTH(Table1[Order Date]) = MONTH(Table1[Ship Date]), 1, 0 )

I'd like to do the whole thing in a measure , but it proved more tricky than I'd have thought, I've tried using datesbetween,

abc:=VAR mdate = MAX(Table1[Order Date]) 
RETURN
CALCULATE([Count of Orders] ,DATESBETWEEN('Calendar'[Date],mdate,EOMONTH(mdate ) ) )

Any suggestions on best way to achieve this welcome,

Richard.