Please give the sample/workbook to your question to be more detailed. It will be easier to find solution.
A lot of the answer depends on what you have on your sheet and in the underlying table.
If you have a way to identify which rows you want to include, you can insert "IF" logic inside the parentheses of the WINDOW_SUM() function. Like this:
WINDOW_SUM( IF ATTR(MONTH[Date]) >=1 and ATTR(MONTH([Date])<= MONTH(TODAY()) THEN SUM([Sales]) END )
This would sum up any rows from January to the current month, for example.
Narendra -- Sorry for the delay getting back to you. The forum's notification function seems to have broken down, so I didn't get notified that you replied here.
So I have your workbook open. What do you want totaled on this sheet?