Period & Ovulation Calculator
Track your cycle, predict ovulation, and understand your fertile window.
Understanding Your Menstrual Cycle
The menstrual cycle is governed by a complex interplay of hormones — mainly estrogen, progesterone, FSH, and LH. Understanding these phases helps you anticipate physical and emotional changes throughout the month.
The Four Phases
1. Menstrual Phase (Days 1-5): The uterine lining sheds. Period bleeding lasts 3-7 days. 2. Follicular Phase (Days 1-13): FSH stimulates follicle growth. Estrogen rises. 3. Ovulatory Phase (Day ~14): LH surges, triggering egg release. This is the most fertile day. 4. Luteal Phase (Days 15-28): Progesterone rises to prepare for potential pregnancy. PMS symptoms may occur.
Cycle Length Variations
The "textbook" 28-day cycle only applies to about 13% of women. Most cycles range from 24-35 days. The luteal phase (after ovulation) is relatively constant at 12-16 days — it's the follicular phase (before ovulation) that varies, which is why ovulation day differs between individuals.
Cycle Predictions
The luteal phase (post-ovulation) is consistently ~14 days. The fertile window is 6 days total.