If my last period started july 18 and i have a 28 day cycle when can i take a pregnancy test. please state date.

Can take it anytime: but the further along in pregnancy the more reliable it is. 2 wk post conception is generally pretty reliably positive. If the periods were absolutely reliable then 4 wks post the last one. But they aren't.... so... 1-2 weeks longer than that might be a reasonable rule of thumb people vary. some ovlulate at very odd intervals. Without an actual examination, I cannot give specific medical advice