rolling year in excel

I have the below statement, which works for a rolling year, how do I adjust
for a rolling 6 month period?

=SUMIF(B6:B52,">="&DATE(YEAR(TODAY())-1,MONTH(TODAY()),1),E6:E52)


Column B6:B52 is my months in MMM-YY format.
Column E6:E52 is $ amounts.
Please help.