According to glow I am 4 weeks 3 days...but 4 weeks and 3 days ago I was on my period and didn't have sex.  The first time we had sex after my period ended (August 31) was on September 6th and 7th. Then again on September 12th and 13th. My cycles have been anywhere from 28 to 32 days since I've been off birth control. So if I go off of the 6th or 7 th or 12th or 13th, then I'm only 2&1/2 or 3&1/2 weeks...and my tests have been very strong - no question about being pregnant. why is the calculation so off??