Average daily data by month

I have a workbook with two sheets - DATA and SUMMARY.
DATA has two columns - date and data_value. Data will be added to this sheet on a regular basis
SUMMARY has two columns - month and average
In the column for average I would like a formula to calculate the average of data_value for each month without having to manually determine the range for the particular month.

Hi and welcome to the board,
one possibility is using a Pivot Table with a Dynamic range
Does the attached file fill your needs ?

Arthurbr,

Thanks for your help

The results of the average for the month are used elsewhere in my actual application so I prefer to NOT use a Pivot table.

In the spreadsheet you provided an array formula as well as the pivot table.

I've modified the array formula from:
{=AVERAGE(IF(MONTH(data!$A$2:$A$66)=MONTH(A4),data!$B$2:$B$66,FALSE))}
to
{=AVERAGE(IF(MONTH(data!$A$2:$A$999)&YEAR(data!$A$2:$A$999)=MONTH(A4)&YEAR(A4),data!$B$2:$B$999,FALSE))}
so that as I add more data over the next year or so the range will be large enough to not need updating AND the average will only be for each month of each year.

SOLVED !!!