The most important part of tracking your menstrual cycle, with or without an app, is recording accurate data and doing this consistently over multiple cycles,” Dr. Kroener says. “The input of period timing, as well as OPK results, cervical mucus changes, physical symptoms, and other pertinent variables, is key.”   After collecting these data points for a few months, the information can indicate to someone what exactly is going on in their cycle. “Typically, ovulation occurs on average 14 days prior to the onset of menses, although there can be some variation,” Dr. Kroener adds. “Analyzing cycle length data in conjunction with the timing of positive LH surge and ovulatory cervical mucus that is wet, stretchy and slippery can help accurately determine how long your cycles are and when ovulation happens relative to expected cycle length.