Computing the monthly mean value from daily data

[Quantopic]

As title suggests, I have to compute the mean of daily values on monthly basis.

The problem consists on the fact that each month has different number of days. I have date data in column A, daily data in column B and I need for computing the arithmetic average for each month in column C.

Can someone can help me?

[6StringJazzer]

How are you laying out column C? To show averages by month, you also need another column telling you what month the average is for. See sample attached. Hopefully you can modify this to suit your format.

[Quantopic]

it has been help to me.
Thanks!
Can I also ask you for computing monthly standard deviation from daily data?