When do women ovulate?

Midcycle: Ovulation almost always occurs 14 days before the menstrual period starts, and the new cycle starts the first day bleeding begins. The normal menstrual cycle can be from 21 to 35 days long. So ovulation can happen anywhere from 7 to 21 days after the period starts - depending on the cycle length. Most women start a period (and new cycle) every 28 to 30 days - so they ovulate 14 to 16 days later.

14d before period: If a woman has a 28 day cycle then she is probably ovulating 1/2 way between or day 14-15 from the start of her last menses. If she has longer cycles - 35-40 days then she will ovulate 14 days before the start of her next period. If her cycles are irregular the best way to check is by using the urine ovulation predictor kit. This will show positive 24 hours prior to ovulation.

Every month...: Usually ovulation occurs midway through the month; usually around day 14 of the menstrual cycle. There are individual differences of course; and some even measure their basal body temperature to pinpoint exactly when(useful in conception attempts).