Successive average

Have you considered adding a column to your source data and doing your calculations there? Then reference that table as your source in the Pivot.

Have a look at Sheet1 revised and then the NewPivot sheet.

I have never attempted it so I don't know. Sorry

The whole point of helper columns is so you CAN use those functions with the Pivot Table, and if it works with the PT it works with slicers since those are nothing more than quick filter

@JBeaucaire:
if i get what the OP wants, i don't think that works because the the average you worked out in the source data is not based on the region. it does not change accordingly to the slicer. for eg. if i choose East in the slicer, i should get 180 because it would be the total time of 900 over just 5 records for Month 4. but yours would still be 189 because total time is still 3,400 over 18 records.

i think the PowerPivot would provide a solution, but i'm unfortunately not up for the job! let me just get OP on the route by activating it:
go to File tab -> Options -> Customize Ribbon -> on the right side, check the option of PowerPivot
convert data in sheet1 into a table. Select A1 & press CTRL + T
while A1 still selected, go to POWERPIVOT tab -> Add to Data Model
you will be brought to this PowerPivot window. Below the data are some cells where you can add something called Measures. This is where someone can hopefully help you with a formula. i am not sure if it's possible to refer to a value in the row labels though. it should go something like this (where i cant figure out the red portion to replace it to look at your month row labels)
AveTime:=CALCULATE(SUM(Table1[Time])/COUNTA(Table1[Time]),Table1[Day of month]<=1)

I assumed it was working because it was giving the same results as the formulas he's added to the page.

Perhaps changing the helper column formula to: =AVERAGEIFS(C:C,B:B, "<="&B2,D:D, D2)

@ benishiryo

I cannot find the PowerPivot option or the addin. Suggestions on where to look? Is it called something else also?

@JBeaucaire:
just a guess on my part though. you could be right. IF i am guessing right again, your new formula doesn't help too because it is now catered only to 1 region. selecting all region or multiple regions now won't work.

@FlameRetired:
i see that your profile states MS-Off Ver 2007 & 2013. PowerPivot is available in the 2013 by default using my steps. in 2010, you have to download it as a free add-in. in 2007, it is not available. you could try this method too:
https://support.office.com/en-us/art...8-fc4798f39ea8

benishiryo thank you for responding. Yes I had found that link in my searches. Regedit is no help either because PowerPivot addin is just not there ... so I went on "safari" and finally found this link.

Read in particular what John Denver and Anita Oakley have to say. The addin is available in Pro Plus version of 2013 only and not Home Office .......

http://answers.microsoft.com/en-us/o...0-db0d187f65c5

Again benishiryo thank you.

Dave