Spread contract value across time

I did not manage with the solution I was following.

I used your code and it works !!!! 

It just look so scary I was afraid to even read it :)

I have code below.

It uses SUMX at the end. 



Total Amount 2 = 
VAR tmpCalendar = ADDCOLUMNS('Calendar',"Month",MONTH([Date]),"Year",YEAR([Date]),"MonthYear",VALUE(YEAR([Date]) & FORMAT(MONTH([Date]),"0#")))
VAR tmpBilling = ADDCOLUMNS('Demand',"MonthYearBegin",VALUE(YEAR([BeginDate]) & FORMAT(MONTH([BeginDate]),"0#")),
                                      "MonthYearEnd",VALUE(YEAR([UntilDate]) & FORMAT(MONTH([UntilDate]),"0#")))
VAR tmpTable = 
SELECTCOLUMNS(
    FILTER(
        GENERATE(
            tmpBilling,
            SUMMARIZE(tmpCalendar,[Year],[Month],[MonthYear])
        ),
        [MonthYear] >= [MonthYearBegin] &&
        [MonthYear] <= [MonthYearEnd]
    ),
    "Customer",[Customer],
    "Year",[Year],
    "Month",[Month],
    "Amount",[Amount]
)
RETURN SUMX(tmpTable,[Amount])