Menstrual Cycle & Ovulation Calculator
Track your menstrual cycle, predict ovulation, fertile window and upcoming periods. Shows current cycle phase, 6-cycle forecast and fertility timeline. Free, private — no data stored.
Enter your last period date to predict your next cycles
The menstrual cycle and ovulation calculator uses the standard luteal phase model to predict ovulation and fertile windows across 6 future cycles. Ovulation is calculated as cycle length minus 14 days (luteal phase = 14 days), following the Naegele-derived framework used in gynecological practice. For a 28-day cycle this places ovulation on day 14; for a 32-day cycle on day 18.
The fertile window spans 6 days: the 5 days before ovulation (sperm viability window) plus ovulation day itself, when the egg is viable for 12-24 hours post-release. The calculator displays four cycle phases — menstrual, follicular, ovulation, and luteal — with the current phase highlighted based on your last period date. All calculations run locally in your browser; no personal health data is transmitted or stored.
⚕️ Important: This tool provides estimates only. Cycles vary due to stress, illness, body weight, and hormonal conditions like PCOS or perimenopause. It is not a contraceptive method (typical failure rate of fertility awareness methods: 24%/year per CDC). Use alongside our Pregnancy Calculator and consult a gynecologist for fertility planning or irregular cycles.
Frequently Asked Questions
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