Predict ovulation and your fertile days across the next several cycles.
Ovulation typically occurs 14 days before the next expected period (the luteal phase is roughly constant at 14 days). For a 28-day cycle that is day 14; for a 35-day cycle it is day 21. The fertile window runs from 5 days before ovulation through ovulation day, because sperm can survive in the reproductive tract for up to 5 days.
Ovulation day
Ovulation day = cycle length − 14
This tool provides estimates based on average cycle patterns and is not a reliable contraceptive method. Consult a healthcare provider for fertility guidance.
No. While the luteal phase is fairly stable, the follicular phase (and therefore ovulation timing) can vary with stress, illness, travel, and other factors. Calendar methods give a statistical estimate, not a guaranteed date.
The day before ovulation and ovulation day itself are the most fertile. The window extends back about 5 days because sperm can survive that long. The egg is viable for only 12–24 hours after ovulation.
Ovulation predictor kits (OPKs) detect the LH surge 12–36 hours before ovulation. Basal body temperature rises by 0.2–0.5 °C after ovulation. Transvaginal ultrasound can directly observe follicle development.