Ovulation Calculator

Your fertile window is the 6-day window ending on the day of ovulation — the 5 days before ovulation plus ovulation day itself. Sperm can survive in the female reproductive tract for up to 5 days, so intercourse before ovulation can still result in conception. The egg is only viable for 12–24 hours after ovulation, but sperm waiting in the fallopian tubes is what creates the longer window. Your most fertile days are the 2–3 days right before ovulation.

Signs of ovulation: (1) Cervical mucus changes to a clear, slippery, egg-white consistency; (2) A slight increase in basal body temperature (BBT) of 0.2–0.5°C after ovulation; (3) Mild one-sided pelvic pain (mittelschmerz); (4) Increased sex drive; (5) Breast tenderness. Ovulation predictor kits (OPKs) detect the LH surge that triggers ovulation 24–36 hours before it occurs. Tracking multiple signs gives the most accurate picture. Calculator estimates are based on average cycle patterns and may not match your body exactly.

Calculators like this one are most accurate for women with regular cycles (within 2–3 days of the same length each month). For irregular cycles, use the average of your last 3–6 cycles as the cycle length input, but understand that your actual ovulation date may vary significantly. If your cycles vary by more than 7 days, tracking physical signs (basal body temperature, cervical mucus, OPK tests) is more reliable. Irregular periods may also indicate underlying conditions like PCOS worth discussing with a doctor.