Hi doc my friend gets her menstruation every 21 days when do she ovulate?

When do I ovulate: Your friend can monitor her basal body temperature by measuring the temperature the first thing in the morning and recording it on a chart. It will appear obvious when ovulation occurs. Also, she can begin a urine LH testing about 21 days before the onset of the expected next menstrual period. The test strip will change color the day before ovulation.