I missed my depo shot four days ago, what ar the chances of getting pregnant in that short of time?

Almost no chance: One can get her Depo-Provera after 11 weeks, and not have to wait for the 12th week. That means getting her shot a week early so she never has to worry about being late for her next shot. Depo-Provera is usually scheduled for every 3 months (every 13 weeks, but getting the shot every 11 to 13 weeks is ok too). The last shot is still working, even if a woman is a few days late for her next shot.