Ovulation Calculator

Ovulation is the release of a mature egg (ovum) from the ovary. It occurs once per menstrual cycle, typically around day 14 of a 28-day cycle (or ~14 days before the next period). The egg survives 12–24 hours after release. Sperm can survive 3–5 days in the reproductive tract, creating a fertile window of about 6 days.

Ovulation typically occurs 14 days before your next expected period. Formula: Ovulation date = First day of next period − 14 days = LMP + (Cycle length − 14). For a 28-day cycle: LMP + 14. For a 32-day cycle: LMP + 18. Our calculator adjusts for your cycle length automatically.

The fertile window is the 6-day period when pregnancy is possible: 5 days before ovulation + the day of ovulation. Sperm can survive up to 5 days, so intercourse in the days leading up to ovulation can result in fertilisation. The most fertile days are the 2–3 days before and including ovulation day.

Ovulation calculators based on cycle length are estimates only. They assume regular cycles and ovulation at a fixed point. Many factors can shift ovulation: stress, illness, travel, hormonal changes, PCOS, breastfeeding, and more. For greater accuracy, use ovulation predictor kits (OPKs) that detect the LH surge, or track basal body temperature (BBT).

Physical signs: Change in cervical mucus (clear, slippery, egg-white texture). Mild cramping or pelvic pain on one side (Mittelschmerz). Slight rise in basal body temperature (0.2–0.5°C) after ovulation. Breast tenderness. Light spotting. Increased libido. An LH surge detected by ovulation predictor kits 24–36 hours before ovulation.

The probability drops dramatically outside the 6-day window, but it's not zero. Cycle irregularity means ovulation can shift, making "safe days" unreliable for contraception. The only reliable method is proper contraception. For family planning purposes, focus on the 5 days before ovulation to ovulation day.

BBT is your lowest body temperature at rest, measured immediately upon waking. Before ovulation, BBT is relatively low (36.2–36.5°C). After ovulation, progesterone causes BBT to rise 0.2–0.5°C, staying elevated until the next period. BBT tracking confirms ovulation has occurred but doesn't predict it in advance. Combined with cervical mucus tracking, it's the fertility awareness method (FAM).

Yes. The luteal phase (post-ovulation to next period) is relatively fixed at ~14 days for most women. It's the follicular phase (period to ovulation) that varies with cycle length. Longer cycles mean later ovulation. A 35-day cycle: ovulation ~day 21. A 24-day cycle: ovulation ~day 10. Our calculator accounts for this.

Yes. Polycystic Ovary Syndrome (PCOS) often causes irregular or absent ovulation (anovulation). Women with PCOS may have very long cycles (35–90+ days) or skip cycles entirely. Standard ovulation calculators are unreliable for PCOS. Consult a gynaecologist or fertility specialist if you have irregular cycles and are trying to conceive.

For couples under 35 having regular unprotected sex: ~30% conceive in the first month, ~75% within 6 months, ~85% within 1 year, ~95% within 2 years. Fertility declines with age. If you haven't conceived after 12 months (or 6 months if over 35), consult a fertility specialist.