Difference between start date and end date

For Case 1:

If start date = month(today()) - 1: use TotalMTD function

For Case 2: 

If the start date and end date are both part of the same month simply the difference in the dates can work.

For case 3:[Bit unclear]

This should go similarly to case 1 by using TotalMTD from 1st March till date.

Hi ChiragGarg2512 , _AAndrade ,thank you for your replies, I'll add further.

Hi GS10 ,

The Table data is shown below:

Please follow these steps:
1. Use the following DAX expression to create a table

Table 2 = CALENDAR(DATE(2024,3,1),DATE(2024,3,31))

2.Creating table-to-table relationships

3.Use the following DAX expression to create a measure

Duration =
VAR _a =
    SELECTEDVALUE ( 'Table'[Start Date] )
VAR _b =
    SELECTEDVALUE ( 'Table'[End Date] )
VAR _c =
    MIN ( 'Table 2'[Date] )
VAR _d =
    MAX ( 'Table 2'[Date] )
VAR _e =
    IF (
        MONTH ( _a ) = 2
            && MONTH ( _b ) = 3,
        DATEDIFF ( DATE ( 2024, 3, 1 ), _b, DAY ),
        IF (
            _a >= _c
                && _b <= _d,
            DATEDIFF ( _a, _b, DAY ),
            IF (
                _b = BLANK ()
                    && CALCULATE ( MONTH ( MAX ( 'Table'[Start Date] ) ) = 2, ALL ( 'Table 2' ) ),
                DATEDIFF (
                    CALCULATE ( MAX ( 'Table'[Start Date] ), ALL ( 'Table 2' ) ),
                    DATE ( 2024, 3, 1 ),
                    DAY
                )
            )
        )
    )
RETURN
    _e

4.Final output

Best Regards,
Wenbin Zhou
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