Peak Day

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 7, 2026

In mucus-based methods (including the Billings Ovulation Method), the last day of fertile-type cervical mucus (characterized as clear, stretchy, or lubricative) correlating closely with the time of ovulation. Peak Day marks the transition point in the mucus pattern from fertile-type to post-ovulatory. In CrMS, Peak Day identification is critical for timing luteal progesterone support in NaPro Medical protocols.⁸

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.