dateadd() is not working as desired to find the date of 7 days from now sql-server -

i trying find date of 7 days specific date. tried

select @fromdate = dateadd(day,-7, max(last_update)), @todate= max(last_update) vwabc

but not working , when tried following every thing works fine.

select @fromdate = '20150601', @todate = max(last_update) vwabc

i cant understand, whats problem. please help.

this worked me through reference stackoverflow question

select @fromdate = convert(date, dateadd(day,-7, max(last_update)),101),  @todate= max(last_update) vwabc

Script