How to Track Your Menstrual Cycle: Calculation, Apps, and Clinical Utility

Cycle Length Calculation

Day 1 = first day of full menstrual flow (not spotting). Count to day before next period starts.

Example: Period starts Jan 1, next starts Feb 1 → 31-day cycle.

Normal Range

21–35 days (average 28). Variation ±7 days is normal. Cycles <21 or >35 days, or sudden change → evaluate.

Tracking Methods

• Calendar or period-tracking apps (Clue, Flo, Ovia, etc.)
• Basal body temperature (BBT) — confirms ovulation retrospectively
• Cervical mucus changes — fertile window (clear, stretchy = egg-white)
• Ovulation predictor kits (LH surge)

Clinical Uses

• Fertility planning (timed intercourse/insemination)
• Contraception (fertility awareness methods)
• Diagnosing PCOS, thyroid, hypothalamic amenorrhea
• Timing prenatal screening, procedures
• Managing PMS/PMDD

Bring 3–6 months of data to your OB/GYN visit for pattern recognition.