There are a few ways to tell that. Some women will experience ovulation pain that is a sharp and intense pain in one or both ovary areas that last a few seconds to a few minutes. These pains may also be accompanied by light cramping or lower back pain. You can also monitor basal body temperature and chart a surge in degrees to know when your ovulating. If all else fails, buy a home ovulation detector kit. They range in price from $12 to $30 dollars and are sold at Walmart, most pharmacies and on line. Good luck!