To echo Kim's assertion about strike selection ....here is another way to dissect whether position is short or long theta and this takes into consideration the skew..... Given 1 exp month, strip out the intrinsic, and net out the "juice" aka extrinisic part, if you are negative, you are bleeding out theta daily. HEre is a snapshot of $147 credit position with a $3 theta coming into your account daily.Both strikes are strictly extrinsic.