Period Calculator

Understanding Your Cycle

A menstrual cycle runs from the first day of one period to the first day of the next. The average is 28 days, but 21-35 days is completely normal.

The Four Phases

• Menstruation (days 1-5): Uterine lining sheds
• Follicular (days 1-13): Estrogen rises, egg develops
• Ovulation (day ~14): Egg released, peak fertility
• Luteal (days 15-28): Progesterone rises, PMS may occur

Tracking Tips

• Log your first day every cycle for 3+ months to find your pattern
• Stress, illness, and travel can shift your cycle