Peak Day

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 11, 2026

Peak Day is the last day in a menstrual cycle on which cervical mucus is clear, stretchy (like raw egg white), or lubricative, and is used as a primary ovulation reference point in mucus-based fertility awareness methods, including the Creighton Model FertilityCare System.¹ Peak Day correlates closely with follicular rupture, occurring within plus or minus two days of ovulation in approximately 95% of cycles.¹ Crucially, Peak Day is identified retrospectively: a woman recognizes it the day after it occurs, when fertile-type mucus has ceased. The day after Peak Day is called post-peak day 1 (P+1). In NaProTECHNOLOGY, Peak Day is the reference anchor for cycle-timed diagnostic blood draws, particularly the post-peak day 7 (P+7) progesterone and estradiol measurements used to evaluate luteal phase adequacy. Accurate Peak Day identification is foundational to NaPro hormonal support protocols and to the diagnostic value of the entire charting system.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.