There are several ways to work out the exact time of ovulation. First, is to keep a calendar. Note your period starting date and finishing date. If your cycle is straightforward, i.e. 28-day cycle, the ovulation day is most likely to be on day 14, i.e. 14 days before the start of your next period. This method is very simple, but can be difficult to predict if your cycle is irregular.

Second way to find ovulation time is to keep a temperature chart. Take your temperature at the same time every morning, e.g. 7am every day, and plot the readings on a chart. Your body temperature will increase slightly after ovulation, and stay same level until your period finishes. So from the chart you can find out when ovulation starts, which is just before the temperature rise. In order to work out an accurate pattern, you need to take readings for several months.

You can also monitor your cervical mucus to find out when you're ovulating. But the easiest and one of the most accurate way (99% accurate) is to use ovulation-predictor kits. You can find those kits in most pharmacies, and you will find they are very easy to use. Simply urinate onto a test-stick each day around the middle of your menstrual cycle, and the kits will detect the increase in luteinizing hormone that predicts your ovulation date.