OPKs are very easy to work with and most come with clear instructions on how to use them. Generally speaking you will test your urine by using the OPK indicator stick in the early afternoon starting around day 9 of your menstrual cycle.
Drinking a little less water in the two hours before you test will increase accuracy. An ovulation predictor kit measures the amount of LH or luteinizing hormone in your urine. LH is at it’s peak about 24 to 36 hours before you ovulate so when the OPK indicates you are at peak fertility definitely try to conceive as soon as possible! Some ovulation predictor kits or “fertility monitors” also measure rising estrogen levels in the blood which can give you a slightly wider fertility window (an additional three days).