How to Sum two values into one Row

Try this measure

Result = 
VAR LastMonthInActuals =
    MAX ( Actual[Month_Num] )
VAR MonthInContext =
    MAX ( Month_Tbl[Month_Num] )
VAR CumulativeTotalOfActual =
    SUMX ( ALLSELECTED ( Actual ), Actual[Value] )
VAR CumulativeMonthlyActuals =
    CALCULATE (
        SUM ( [Value] ),
        FILTER ( ALLSELECTED ( Actual ), Actual[Month_Num] <= LastMonthInActuals )
    )
VAR CumulativeForecast =
    SUMX (
        FILTER (
            ALL ( Forecast ),
            Forecast[Month_Num] > [LastMonthInActuals]
                && Forecast[Month_Num] <= MonthInContext
        ),
        Forecast[Value]
    )
RETURN
    IF (
        MonthInContext <= LastMonthInActuals,
        CumulativeMonthlyActuals,
        CumulativeForecast + CumulativeTotalOfActual
    )

Anonymous 

Thank you so much for the measure, the result was wrong but I modified it and it works :)

See measure in Red. Your original measure was Forecast[Value], I replaced with Forecast[Forecast_Var])

Forecast_Var = CALCULATE(SUM(Forecast[Value]),
                FILTER(Forecast, Forecast[Month_Num] >= MONTH(TODAY())))

This is the final measure

Measure = 
VAR LastMonthInActuals = MAX ( Actual[Month_Num] )
VAR MonthInContext = MAX ( Month_Tbl[Month_Num] )
VAR CumulativeTotalOfActual = SUMX ( ALLSELECTED ( Actual ), Actual[Value] )
VAR CumulativeMonthlyActuals = CALCULATE (SUM ( Actual[Value] ),FILTER ( ALLSELECTED ( Actual ), Actual[Month_Num] <= LastMonthInActuals ))
VAR CumulativeForecast = SUMX (FILTER (ALL ( Forecast ),Forecast[Month_Num] > LastMonthInActuals && Forecast[Month_Num] <= MonthInContext), Forecast[Forecast_Var])
RETURN
    IF (
        MonthInContext <= LastMonthInActuals,
        CumulativeMonthlyActuals,
        CumulativeForecast + CumulativeTotalOfActual)

This the result and it summing correctly.

Thank you so much y'all. :)