Predict your next period, ovulation window and fertile days. Based on the standard 14-day-before-next-cycle calculation.
The menstrual cycle is divided into four hormone-controlled phases: menstrual (endometrium shedding), follicular (ovarian follicle growth driven by FSH), ovulatory (LH surge triggers egg release) and luteal (corpus luteum produces progesterone to prepare for pregnancy).
Ovulation typically occurs 14 days before the start of the next period — not necessarily on day 14 of the cycle. For a 28-day cycle, ovulation occurs on day 14; for a 35-day cycle, on day 21.
The fertile window starts 5 days before ovulation (because sperm survive up to 5 days in the female reproductive tract) and ends 1 day after ovulation (the egg is viable for 12–24 hours). Therefore, the fertile window is approximately 6 days.
A "regular" cycle is defined as one with consistent duration between 21 and 35 days, with less than 7 days variation between cycles. Irregular cycles (variation > 7 days) are common and may be caused by PCOS (polycystic ovary syndrome), thyroid disorders, intense stress, rapid weight loss or excessive exercise.
Consult a healthcare professional if you experience: absence of menstruation for 3+ months (amenorrhea), cycles shorter than 21 or longer than 35 days, very heavy bleeding (changing a pad every hour), intense pelvic pain, or bleeding between periods.