tarajanes is correct. Based on your cycle length, count backwards 14-16 days to find out your ovulation day. However, if you have wacky cycles, like me, anywhere from 28-37 days long, you may want to use ovulation tests to find out for sure. You can buy a big pack of them and use them like you would pregnancy tests.
It dont matter when you start your period,to work out ovulation calculate how long your periods are.ie 28 days,32,etc. then count back 14 days from the day you start.this will tell you when you ovulated.remeber if your cycle is every 28 days,pretty much so ovulation will occur cd14.
so as a guide its 14 days before your next period is due.give or take a day or 2.every women has a 25% chance every month of concieveing,provideing no complications.