Trailing 12 months DAX

BItoken , You formula seems correct, you need use MAx of date. End of month will not apply in your case

Trailing 12 Months = CALCULATE(SUM(Table[Sales]), DATESINPERIOD(Date[Date],Max(Date[Date]),-4,QUARTER))

or

Trailing 12 Months = CALCULATE(SUM(Table[Sales]), DATESINPERIOD(Date[Date],Max(Table[Date]),-4,QUARTER))

Always use date table. As solution might work without that, but will create issue in future.

To get the best of the time intelligence function. Make sure you have a date calendar and it has been marked as the date in model view. Also, join it with the date column of your fact/s. Refer :
https://radacad.com/creating-calendar-table-in-power-bi-using-dax-functions
https://www.archerpoint.com/blog/Posts/creating-date-table-power-bi
https://www.sqlbi.com/articles/creating-a-simple-date-table-in-dax/

Appreciate your Kudos.

Hi BItoken ,

I created a sample pbix file for you, please check if that is what you want.

1. Create a calculated column to order by the data base on the fiscal quarter

Rank = RANKX ( 'Sales', 'Sales'[Fiscal Qtr],, ASC, DENSE )

2. Create a measure to get the rolling 4 quaraters sales

Trailing 12 Months = 
VAR _index = MAX ( 'Sales'[Rank] )
VAR _date =  MAX ( 'Sales'[Date] )
RETURN
    CALCULATE (
        SUM ( 'Sales'[Sales] ),
        FILTER (
            ALL ( 'Sales' ),
            'Sales'[Rank] >= _index - 3
                && 'Sales'[Rank] <= _index
                && 'Sales'[Date] <= _date
        )    )

Best Regards

Rena