Birth's Ovulation Calculator will tell you when you are releasing an egg each month (also known as ovulating), and therefore when you are most fertile. You'll need to have sexual intercourse on these days in order to have the best chances of conceiving.
Ovulation can also be detected by using a combination of physical observations, including counting the days of your menstrual cycle, taking your temperature and/or looking for specific physical signs. You can learn more about conception here.
Ovulation Calculator