Find your fertile window and most likely ovulation date. Enter your last period date and average cycle length to get personalized predictions.
Enter the first day of your last menstrual period, your average cycle length (the number of days from the start of one period to the start of the next), and your typical period length. The calculator will identify your fertile window and most likely ovulation date.
The fertile window is typically days 10–17 of a 28-day cycle. Sperm can survive in the reproductive tract for up to 5 days, so conception is possible in the days before ovulation as well as on the ovulation day itself.
Ovulation typically occurs about 14 days before the start of the next period. For a 28-day cycle, that's around day 14. For a 32-day cycle, it would be around day 18. This calculator uses that formula to estimate your ovulation date:
The fertile window spans from 5 days before ovulation through 1 day after.
The best time to conceive is during the fertile window — the 5–6 days around ovulation. The days immediately before ovulation and the day of ovulation itself offer the highest probability of conception. Since sperm can live up to 5 days, having sex in the days leading up to ovulation is also effective.
Signs of ovulation include a change in cervical mucus (becoming clear and slippery, like egg whites), a slight rise in basal body temperature, mild one-sided pelvic pain (mittelschmerz), and a positive result on an ovulation predictor kit (OPK). Tracking these signs alongside calendar predictions improves accuracy.
If your cycle varies by more than a few days month to month, calendar-based predictions become less reliable. In this case, ovulation predictor kits, basal body temperature tracking, or a conversation with your OB-GYN will give you more accurate information about your personal ovulation pattern.
It's uncommon but possible. Women with shorter cycles (21–24 days) may ovulate soon after their period ends. Since sperm can survive several days in the reproductive tract, unprotected sex during or just after a period could potentially result in conception for women with short cycles.