The problem is you can never be sure when you ovulate, and some experts say it should be around day 14 of your cycle, but thats only if you have a perfect 28 day cycle which most women dont........the month I fell pregnant I ovulated on day 7 and the month previously on day 17 (mainly due to coming off the pill).
You need to look out for signs - changes in CM being the most significant. I used to get horrendous pains and upset stomach at the time of ovulation.
You can in effect conceive within a 5 day window, so a number of days before ovulation and then the day after you ovulate, as sperm can survive for a number of days and lie in wait for the egg.
You can also use ovulation prediction kits (very cheap on ebay for a bumper pack), which can also assist in telling you when you are about to ovulate!
Good Luck TTC.....