Outstanding amount with drill up

Hi all,

I hope someone can help me out. I am trying to do the following:

In the dataset, I have a table named 'loan_balance'. In this loan balance table there can be multiple records for one loan number with the corresponding outstanding amount in the same row.

Each row has a valid_from and valid_to date.

I then made a table to plot all the outstanding amount for each loan number for each date in the calander table:

Lening balans historie = 
filter(
GENERATE(ALLNOBLANKROW('Kalender werkvoorraad'[Datum]),
CALCULATETABLE(
var meetdatum = SELECTEDVALUE( 'Kalender werkvoorraad'[Datum])
 
var temptabel = 
filter('Lening balans', 'Lening balans'[credit_balance_valid_from] <= meetdatum &&
('Lening balans'[credit_balance_valid_to] > meetdatum || isblank('Lening balans'[credit_balance_valid_to]))
&& 'Lening balans'[credit_valid_from] <= meetdatum &&
('Lening balans'[credit_valid_to] > meetdatum || isblank('Lening balans'[credit_valid_to]))) 


return selectcolumns(temptabel, "source loan part id", 'Lening balans'[source_loan_part_id], "outstanding amount", 'Lening balans'[outstanding_amount])
)
), [outstanding amount] <> 0)

This table has a relationship with my general calander table. In this calender table there is a date hierarchy.

I then made a measure to determine the outstanding amount:

calculate(SUM('Lening balans historie'[outstanding amount]), USERELATIONSHIP(Kalender[Datum],'Lening balans historie'[Datum]))

This works when I show the information on date level. But once I drill up to week or month level, this does not work well.. This is because the outstanding amount is plotted for each date, so the outstanding amount will summarize, also for each date within the month (although the amount for example stayed the same). 

How can I make this work on week or month level?