I have one row filled with dates in the format MM/dd/yyyy (with header row), such as:
DATES
5/12/2015
4/12/2012
5/7/2015
5/7/2014
I would like
You can use COUNTIFS
like this
=COUNTIFS(A:A,">="&EOMONTH(TODAY(),-1)+1,A:A,"<"&EOMONTH(TODAY(),0)+1)
That works equally well in Excel or google sheets, for the whole column and will ignore the header row
In Google sheets you can use
=COUNT(FILTER(A:A,MONTH(A:A) = MONTH(TODAY()),YEAR(A:A)=YEAR(TODAY())))
Where A:A is the column with your dates
With data in A1 through A20
=SUMPRODUCT((MONTH(A1:A20)=MONTH(TODAY()))*(YEAR(A1:A20)=YEAR(TODAY())))