Ovulation & Fertility Calculator
Calculate your estimated ovulation day and fertile window.
📐 Ovulation ≈ Cycle Length − 14 days after LMP. Fertile window = 5 days before to 1 day after ovulation. Estimate only — actual ovulation varies by individual.
The ovulation calculator estimates your most fertile days based on your menstrual cycle. Understanding your fertility window — the days when conception is most likely — is valuable whether you are trying to conceive or tracking your cycle for family planning. This calculator uses the standard method based on average cycle length to predict ovulation, the fertile window (5 days before ovulation plus ovulation day), and expected period dates for the next 3 months.
📋 How to Use This Calculator
Enter the date your last period started and your average cycle length (21–35 days; 28 days is average). Click Calculate to see your predicted ovulation date, the 6-day fertile window, and your next expected period date. The fertile window is highlighted because sperm can survive up to 5 days inside the female reproductive tract, so intercourse before ovulation can result in conception. For the most accurate results, track your cycle over 3–6 months to establish your personal average.
💡 Key Facts & Information
Ovulation typically occurs 14 days before the next period, regardless of cycle length. A 28-day cycle: ovulation around day 14. A 32-day cycle: ovulation around day 18. A 24-day cycle: ovulation around day 10. The luteal phase (ovulation to period) is relatively constant at 12–16 days. Signs of ovulation include: cervical mucus becoming clear and stretchy (egg-white consistency), a slight rise in basal body temperature (0.2–0.5°C), mild one-sided pelvic pain (mittelschmerz), and a positive result on an LH surge ovulation predictor kit (OPK). Irregular cycles make prediction less reliable — conditions like PCOS, thyroid disorders, and stress can disrupt ovulation.