Understanding the fertile window
An egg survives 12-24 hours after ovulation. But sperm can survive in the fallopian tubes for up to 5 days. So your fertile window opens about 5 days before ovulation and closes the day after. The two days before ovulation and ovulation day itself carry the highest pregnancy probability.
Ovulation typically occurs 14 days before the next period, not 14 days after the last one. That distinction matters for anyone with a cycle longer or shorter than 28 days. A 35-day cycle means ovulation around day 21, not day 14.
Signs of ovulation
Cervical mucus becomes clear, stretchy, and egg-white in consistency around ovulation. Some women experience mild one-sided pelvic pain (mittelschmerz). Basal body temperature rises by 0.2-0.5°C after ovulation and stays elevated until the next period. Ovulation predictor kits (OPKs) detect the LH surge that precedes ovulation by 24-36 hours.
Cycle variation
Calculator-based ovulation prediction assumes a regular cycle. In practice, cycle length varies month to month, particularly under stress, illness, or significant weight change. If cycles vary by more than 7 days, calendar-based methods are unreliable and LH testing or fertility monitoring is more accurate.
Related tools
If conception is successful, calculate your due date with the Due Date Calculator. For menstrual cycle tracking and irregularities, see Menstrual Cycle Calculator. For gestational weight management, see Gestational Weight Gain.