A: If you have a regular 28-day cycle, ovulation usually occurs on day 14 of the cycle - day one being the day menstruation begins. However, as sperm survive for up to 72 hours, your most fertile period is three days before and after day 14, meaning day 11 to day 17.
If, however, you have a regular 30-day cycle, then you assume that ovulation occurs always nearly 14 days before the next menstruation. Therefore your fertile period would be on day 16, plus or minus three days.
To pinpoint when ovulation will occur, you can test your urine to see how much the urinary luteinising hormone levels have risen.
The hormone helps regulate the menstrual cycle and egg production. It increases rapidly just before ovulation - about 36 hours before.
The chance of pregnancy is about 25 per cent should you try at the time of ovulation.