Sum of Values based on date field

[Arvind_07]

Hello all, 

For the below table, I intend to use an KPI measure to show MTD Sales. But the MTD Sales should show the summary of values until last week. For getting the last week data, I use the expression =if(getselectedcount(Date)=0,num(WeekStart(today()-7)),Date). But I want to use this expression to get the MTD Sales on the KPI measure for last week.

Could you please help me with an expression to get the sum of MTD Sales for last week for the KPI measure

Thank you

Product Group	Week Number	Year	Month	Date	MTD Sales Units
A Box	W01 2020	2020	Jan 2020	2019-12-29	41
A Box	W02 2020	2020	Jan 2020	2020-01-05	146
A Box	W03 2020	2020	Jan 2020	2020-01-12	284
A Box	W04 2020	2020	Jan 2020	2020-01-19	410
A Box	W05 2020	2020	Jan 2020	2020-01-26	629
A Box	W06 2020	2020	Feb 2020	2020-02-02	169
A Box	W07 2020	2020	Feb 2020	2020-02-09	289
A Box	W08 2020	2020	Feb 2020	2020-02-16	533
A Box	W09 2020	2020	Mar 2020	2020-02-23	189

[Vegar]

You could try an expression like this:

Sum({< WeekNumber, Year, Month,[Date]={">=$(=MonthStart(today(),-1))<$(=weekstart(today()))"}>}[MTD Sales Units])

[Arvind_07]

is it possible to get the above expression with Weekstart(today()-7) function alone? because my calendar month start and end dates are different than normal calendar