How can I calculate a rolling average in DAX/PowerBI? - powerbi

Question

After going through several posts on StackOverflow and the PowerBI forums, I still can't figure out how to calculate a rolling average based on a given period- in my case, a 30-day rolling average.
Most of the posts I've seen advocate something either identical or really similar to this:
Rolling Sum :=
CALCULATE (
[Sales],
FILTER (
ALL ( Sales ),
[Date]
>= MAX ( Sales[Date] ) - 365
&& [Date] <= MAX ( Sales[Date] )
)
)
(code taken from this post)
...and yet, I can't seem to get the proper values.
In my case, I have the following:
"closing date" for a given loan (column)
loan count (measure)
closing length (column)- length of time (in days) to close a loan
What I'd like to calculate is the rolling 30 day average for any given day. I coded the following:
Rolling Average =
CALCULATE (
SUM(Query1[Closing_Length])/[Loan Count],
FILTER (
ALL ( Query1 ),
[Closing Date].[Date]
>= MAX ( Query1[Closing Date] ) - 30
&& [Closing Date] <= MAX ( Query1[Closing Date] )
)
)
To check the results, I used a visual filter to examine one month's worth of data and these are the results:
Note the totals row at the bottom; for this given period, there are 102 loans and it took an aggregate of 3922 days for them to close. The average I'd like to calculate is 3922/102, which should equal approximately 38.45 days. Instead, we see 42.
How can I fix this?

Answer 1

Measure based solution:
Rolling Average Measure =
VAR A =
SUMX (
FILTER (
ALL ( 'Query' ),
'Query'[Closing Date] <= MAX ( 'Query'[Closing Date] )
),
ROUND ( 'Query'[Closing Length], 2 )
)
VAR B =
SUMX (
FILTER (
ALL ( 'Query' ),
'Query'[Closing Date] <= MAX ( 'Query'[Closing Date] )
),
ROUND ( 'Query'[Loan Count], 2 )
)
RETURN
A / B
Calculated column based solution:
Rolling Average =
VAR CurrentDate = 'Query'[Closing Date]
VAR T =
FILTER ( 'Query', [Closing Date] <= CurrentDate )
RETURN
ROUND ( SUMX ( T, 'Query'[Closing Length] ) / SUMX ( T, [Loan Count] ), 2 )
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