A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
I made a whole lot of assumptions that would affect
the method and results of the solution.
To make a better fit please specify:
Is you data a bookkeeping record of financial transactions like mine?
Do you want the average of multiple daily transactions or
the average of the sum of monthly transactions?
Do you enter no transactions as zero or blank or skip the date?
If the daily or monthly transactions add up to zero,
do you ignore the zero?
An upload of a huge sample at MediaFire.com would be helpful.