Incorrect Total

Hi Anonymous 
Please try

Ans =
SUMX (
    VALUES ( 'Table'[YearMonth] ),
    CALCULATE (
        VAR RemDays =
            MAXX ( 'Plan', [Rem_Cnt] )
        VAR ActDays =
            MAXX ( 'Plan', [Day_Cnt] ) - RemDays
        VAR Result =
            CALCULATE (
                SUMX ( 'Details', DIVIDE ( [MyValue], ActDays ) * RemDays ),
                MyDim[DimValue] <> "Do not want this"
            )
        RETURN
            Result
    )
)

Anonymous Adding my standard reply here in hopes you will vote for the idea. But please mark tamerj1's post a the solution if it solves your problem.

First, please vote for this idea: https://ideas.powerbi.com/ideas/idea/?ideaid=082203f1-594f-4ba7-ac87-bb91096c742e

This looks like a measure totals problem. Very common. See my post about it here: https://community.powerbi.com/t5/DAX-Commands-and-Tips/Dealing-with-Measure-Totals/td-p/63376

Also, this Quick Measure, Measure Totals, The Final Word should get you what you need:
https://community.powerbi.com/t5/Quick-Measures-Gallery/Measure-Totals-The-Final-Word/m-p/547907

Also: https://youtu.be/uXRriTN0cfY
And: https://youtu.be/n4TYhF2ARe8