Hmm, I would rather do this in the SQL code ...

I scrapped up the following >>

with cte as

(

selectcast('20140701' as date) as cteDate

Union all

selectdateadd(d, 1,c.cteDate)

fromcte as c

wherec.cteDate <'20140731'

)

,nextCte as

(

select top 1

cteDate,

min(cteDate) Over (Partition by NULL) as minDate,

max(cteDate) Over (Partition by NULL) as maxDate

from cte

)

Select

minDate,

maxDate,

datediff(d, minDate, maxDate) as numDaysBetween,

dateadd(d, datediff(d, minDate, maxDate)/2,minDate) as averageDate

from nextCte

If gives me the average day of 7/16 for the month of July. You may need to do some tweaking for when the number of days between divided by two is not a whole number (like employ datetime instead of date). See if this gets you going.