monthly average each year

osamashokeir 

This solves the issue:

How it works: 

1. Write first Date of each month for respected years in Column E & apply cell format mmm-yyyy.
2. Enter this formula in cell F39 & fill down.

=IFERROR(AVERAGEIFS($C$39:$C$58,$B$39:$B$58,">="&$E39,$B$39:$B$58,"<="&EOMONTH($E39,0)),0)

N.B.

1. Formula returns ZERO for moths, are not available in Column B.

You may use this formula also:

=IFERROR(SUMPRODUCT((MONTH($B$39:$B$58)=MONTH(E39)*(YEAR($B$39:$B$58)=YEAR(E39)))*($C$39:$C$58))/(SUMPRODUCT((MONTH($B$39:$B$58)=MONTH(E39)*(YEAR($B$39:$B$58)=YEAR(E39)))*1)),0)

Accept this as Best response as well Like, if my post solves the issue.