Average date difference between two dates in same column

Hi Anonymous 

Sorry for replying late.

Please create measures

lastmonth = CALCULATE(MAX('date'[year-month]),FILTER(ALLSELECTED('Table'),'Table'[CustomerID]=MAX('Table'[CustomerID])))

measure in days =
VAR days1 =
    CALCULATE (
        SUM ( 'date'[days_m] ),
        VALUES ( 'date'[year-month] ),
        FILTER (
            ALLSELECTED ( 'Table' ),
            'Table'[CustomerID]
                = MAX ( 'Table'[CustomerID] )
        )
    )
RETURN
    IF (
        [lastmonth]
            = MAX ( 'date'[year-month] )
            && [lastmonth]
                <> BLANK (),
        MAX ( 'date'[days_m] ) / 2,
        days1
    )


each days = SUMX(FILTER(ALLSELECTED('Table'),'Table'[CustomerID]=MAX('Table'[CustomerID])),[measure in days])

average dyas = SUMX(ALLSELECTED('Table'),[measure in days])/2

The date table used above

date =
ADDCOLUMNS (
    CALENDARAUTO (),
    "year", YEAR ( [Date] ),
    "month", MONTH ( [Date] ),
    "year-month", FORMAT (
        [Date],
        "yyyy-mm"
    )
)

add a column in date table
days_m = CALCULATE(COUNT('date'[Date]),ALLEXCEPT('date','date'[year-month]))

Best Regards
Maggie
Community Support Team _ Maggie Li
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

Hi Anonymous 

Is this ok?

lastmonth =
CALCULATE (
    MAX ( 'date'[year-month] ),
    FILTER (
        ALLSELECTED ( 'Table' ),
        'Table'[CustomerID]
            = MAX ( 'Table'[CustomerID] )
            && 'Table'[country]
                = MAX ( 'Table'[country] )
    )
)

measure in days =
VAR days1 =
    CALCULATE (
        SUM ( 'date'[days_m] ),
        VALUES ( 'date'[year-month] ),
        FILTER (
            ALLSELECTED ( 'Table' ),
            'Table'[CustomerID]
                = MAX ( 'Table'[CustomerID] )
                && 'Table'[country]
                    = MAX ( 'Table'[country] )
        )
    )
RETURN
    IF (
        [lastmonth]
            = MAX ( 'date'[year-month] )
            && [lastmonth]
                <> BLANK (),
        MAX ( 'date'[days_m] ) / 2,
        days1
    )


each days =
SUMX (
    FILTER (
        ALLSELECTED ( 'Table' ),
        'Table'[CustomerID]
            = MAX ( 'Table'[CustomerID] )
            && 'Table'[country]
                = MAX ( 'Table'[country] )
    ),
    [measure in days]
)


total eachdays =
IF (
    ISINSCOPE ( 'Table'[CustomerID] ),
    [each days],
    AVERAGEX (
        SUMMARIZE (
            'Table',
            'Table'[CustomerID],
            "m", [each days]
        ),
        [m]
    )
)

Best Regards

Maggie