Average of difference between columns with filters

[Ritaf]

Hi,

I have a table as on the picture and need to calculate the average difference between the start date and the end date, by supplier excluding rows with a start date after the end date and excluding rows whose start date/end date is"31/12/1899".
I tried the dax below, but it gives me incorrect results, how can I correct it?

TestAverage =

CALCULATE(AVERAGEX('Sheet1',

DATEDIFF('Sheet1'[StartDate],Sheet1[EndDate],DAY)),

FILTER(Sheet1,Sheet1[StartDate]<Sheet1[EndDate] && Sheet1[StartDate]<>31/12/1989 && Sheet1[EndDate]<>31/12/1989))
Link to Samle File:Sample.pbix 

[Ritaf]

It worked !! Thank you!

[Jihwan_Kim · Accepted solution]

Hi,

Please try the below measure.

TestAverage =
AVERAGEX (
    FILTER (
        Sheet1,
        Sheet1[StartDate] < Sheet1[EndDate]
            && NOT ( Sheet1[StartDate] = DATE ( 1899, 12, 31 ) )
                && NOT ( Sheet1[EndDate] = DATE ( 1899, 12, 31 ) )
    ),
    DATEDIFF ( 'Sheet1'[StartDate], Sheet1[EndDate], DAY )
)