Ovulation Predictor Kits (OPKs) are tools used to help individuals identify their fertile window in the menstrual cycle. These kits work by detecting the surge of luteinizing hormone (LH) in urine, which typically occurs 24 to 36 hours before ovulation. By using OPKs, individuals can better time intercourse to increase the chances of conception. OPKs come in various forms, including test strips and digital devices. Users typically begin testing a few days before they expect ovulation, based on their cycle length. The results indicate whether the LH surge is present, helping to pinpoint the most fertile days for conception.