I am very new to DAX and i want sum of sales for the previous months. As you can see, the dates are : The 15th of every month and the last day of every month. Can anyone please help me?

I want when i use the date as a filters , when i chose a date, i want the measure to give me the results of the previous date.

![image](https://i.stack.imgur.com/OoAos.png)