How To Calculate Ovulation Period?

well i was late on my period this month. so we thought i was pregnant and we were hoping for one. but comes up tht i might not be because i have my period. so i was woundering when do i ovlate because ive been reading and trying to find out and the say only 28 days for a period and i only go for 7 days so i need to know when do you think i would ovlate