Ovulation Calculator

Ovulation occurs approximately 14 days before your next expected period — regardless of cycle length. For a 28-day cycle: around day 14. For a 30-day cycle: around day 16. For a 35-day cycle: around day 21. The post-ovulatory phase (ovulation to next period) is relatively constant at 12–16 days; it's the pre-ovulatory phase that varies.

The fertile window is the 6 days during which sex can result in pregnancy: the 5 days before ovulation plus ovulation day itself. Sperm can survive up to 5 days in the reproductive tract, while an egg is viable for only 12–24 hours after release. Peak fertility is the 2–3 days just before ovulation.

Common signs: cervical mucus becomes clear, slippery, and stretchy (like raw egg white) in the days before ovulation. Basal body temperature (BBT) drops slightly just before ovulation then rises 0.2–0.5°C afterwards, confirming it occurred. Some women experience mittelschmerz — mild one-sided pelvic pain during ovulation. LH surges 24–36 hours before ovulation (detected by ovulation predictor kits).

Calendar-based calculators are estimates based on average cycle patterns — they assume regular cycles and constant luteal phase length. Actual ovulation varies with stress, illness, travel, sleep disruption, and medications. For TTC (trying to conceive) or contraception, combine calendar tracking with BBT charting and/or OPK (ovulation predictor kit) testing for higher accuracy.

It is unlikely but not impossible. The fertile window is a statistical approximation — ovulation can shift with cycle irregularity. For this reason, calendar-based tracking alone is not a reliable contraception method (typical use failure rate ~24%). For contraception, use a dedicated fertility awareness method with training or a reliable contraceptive method.