Sum value between start date and end date

Hi EVBI,

Please refer to below steps:

1. I am not sure which column is the unique column in source table, so I first added an Index column in Query Editor mode. 

2. Create a calendar table.

Dim date Tb = CALENDAR(DATE(2018,1,1),DATE(2018,12,31))

Days per month =
CALCULATE (
    DAY ( MAX ( 'Dim date Tb'[Date] ) ),
    ALLEXCEPT (
        'Dim date Tb',
        'Dim date Tb'[Date].[Year],
        'Dim date Tb'[Date].[Month]
    )
)

3. Cross Join calendar table and fact data table, and add below calculated columns.

Cross Join Tb =
ADDCOLUMNS (
    FILTER (
        CROSSJOIN ( 'Dim date Tb', data ),
        'Dim date Tb'[Date] >= [start date]
            && 'Dim date Tb'[Date] <= [end date]
    ),
    "Year", YEAR ( [Date] ),
    "Month", MONTH ( [Date] )
)

Count days =
CALCULATE (
    COUNT ( [Date] ),
    ALLEXCEPT (
        'Cross Join Tb',
        'Cross Join Tb'[Year],
        'Cross Join Tb'[Month],
        'Cross Join Tb'[Index]
    )
)

Actual Rev =
'Cross Join Tb'[Count days] / 'Cross Join Tb'[Days per month]
    * 'Cross Join Tb'[Net Rev(USD)]

4. Summarize above table.

Summarize Tb =
SUMMARIZE (
    'Cross Join Tb',
    'Cross Join Tb'[Year],
    'Cross Join Tb'[Month],
    'Cross Join Tb'[Index],
    "Net Rev", AVERAGE ( 'Cross Join Tb'[Actual Rev] )
)

5. Below calculated table is the final output.

Summarize Tb2 =
SUMMARIZE (
    'Summarize Tb',
    'Summarize Tb'[Year],
    'Summarize Tb'[Month],
    "Sum Rev per month", SUM ( 'Summarize Tb'[Net Rev] )
)

Best regards,

Yuliana Gu