Previous Dynamic Period DAX Calculation

[mark_carlisle]

I've followed the guide on https://radacad.com/previous-dynamic-period-dax-calculation for creating a dynamic previous period. So if I select a date range for the current period of;

• 01/06/2019 to 01/06/2019 the previous period is 31/05/2019 to 31/05/2019
• 01/06/2019 to 02/06/2019 the previous period is 30/05/2019 to 31/05/2019
• 01/06/2019 to 07/06/2019 the previous period is 25/05/2019 to 31/05/2019
• 01/06/2019 to 30/06/2019 the previous period is 02/05/2019 to 31/05/2019
• 01/04/2019 to 30/06/2019 the previous period is 31/12/2019 to 31/03/2019

However the StartOfPreviousPeriod measure is not ideal for me. For example, selecting a date range of 01/06/2019 to 30/06/2019 for the current period means that the StartOfPreviousPeriod is 02/05/2019, as in the example above.

StartOfPreviousPeriod =
FIRSTDATE (
    PREVIOUSDAY (
        DATEADD ( CalendarCombined[Date], -1 * [DaysInCurrentPeriod], DAY )
    )
)

However what I would like to do is have the date show as 01/05/2019 but I cannot figure out a way without breaking the dynamic elements of it. For clarity, using the examples supplied above if I select a date range for the current period of;

• 01/06/2019 to 01/06/2019 the previous period should be 31/05/2019 to 31/05/2019
• 01/06/2019 to 02/06/2019 the previous period should be 30/05/2019 to 31/05/2019
• 01/06/2019 to 07/06/2019 the previous period should be 25/05/2019 to 31/05/2019
• 01/06/2019 to 30/06/2019 the previous period should be 01/05/2019 to 31/05/2019
• 01/04/2019 to 30/06/2019 the previous period should be 01/01/2019 to 31/03/2019

Any assistance would be greatly appreciated.

[parry2k · Accepted solution]

@mark_carlisle seems like you have two logic going on, and you want if selection is full month then use full previous month.

so you can build a logic like, if first selected date is first date of the month and last selected date is last date of the month, full month is selected and then use this in if condition with PreviousMonth DAX function.

[parry2k · Accepted solution]

@mark_carlisle seems like you have two logic going on, and you want if selection is full month then use full previous month.

so you can build a logic like, if first selected date is first date of the month and last selected date is last date of the month, full month is selected and then use this in if condition with PreviousMonth DAX function.

[mark_carlisle · Accepted solution]

Yeah I figured that was going to be the case, was hoping there was going to be some time intelligence DAX function I might have missed. The following is what I've went with;

StartOfPreviousPeriod =
IF (
    AND (
        FIRSTDATE ( CalendarCombined[Date] ) = STARTOFMONTH ( CalendarCombined[Date] ),
        LASTDATE ( CalendarCombined[Date] ) = ENDOFMONTH ( CalendarCombined[Date] )
    ),
    FIRSTDATE (
        PREVIOUSMONTH (
            DATEADD ( CalendarCombined[Date], -1 * [MonthsInCurrentPeriod], MONTH )
        )
    ),
    FIRSTDATE (
        PREVIOUSDAY (
            DATEADD ( CalendarCombined[Date], -1 * [DaysInCurrentPeriod], DAY )
        )
    )
)