How To Compare 2 Date By Month?

I'm doing DTS, Here is one of my Sql Query in DTS

 

Select * From ZT_DailyRpt_Detail
 Where
isNumeric(TenDayDate) = 1 And TenDayDate <
Convert(varchar(10),DateAdd(Month,-CAST
                              ((SELECT         keepmonth
                                  FROM             zt_databackup a, zt_biller b
                                  WHERE         a.companycode = b.companycode AND
                                                            zt_DailyRpt_Detail.biller_code = b.billercode) AS int),GetDate()),112)

 

the sub query �?SELECT         keepmonth
                                  FROM             zt_databackup a, zt_biller b
                                  WHERE         a.companycode = b.companycode AND
                                                            zt_DailyRpt_Detail.biller_code = b.billercode) AS int】will return a value 6 or 12

for the reason, every month have differnet days, ( some have 31 days , some are 30 days ) I don't want to check the day of date , only to compare month 

if sub query return "6" and I do DTS on 2007/07/29 , will select  date which TenDayDate< 2007/01 not  TenDayDate<2007/01/29 ( don't want to check the day of date)

 

does my query correct? if not can you correct it for me? thank you very much