date formula working inconsistently

[Benjwill]

Hi everyone, could you help me with this?

I created a measure to display the start date depending on the end date selected in the filter, and the period selected on my slicer (1 month, 3 months, etc). Both start date and end date are always end of month from my calendar table. 

My dax formula for end date:  SELECTEDVALUE(DIM_Calendar[End of Month])

My dax formula for start date (in this case the date 6 months before): DATEADD(DIM_Calendar[End of Month],-6,MONTH)
 

when the end date filter is 31 August 2024, my measure correctly displays the start date as 29 Feb 2024 (yellow highlighted): 

But when I selected my end date as 30 Sept 2024, my measure stopped working.  

Does any one know how I could fix it? Should I not use dateadd as the formula?

Thank you in advance!!!

[Benjwill]

Hi Johnt75, this solution works! Thank you very much for your help.

[johnt75 · Accepted solution]

Try

Start Date = EOMONTH( [End Date], -6 )

where [End Date] is your existing end date measure.