Estimate your most fertile days and likely ovulation date from your last period and cycle length.
Ovulation typically happens about 14 days before your next period starts — so for a 28-day cycle, that's day 14. This calculator adjusts that timing based on your actual average cycle length.
The fertile window includes the 5 days before ovulation plus ovulation day itself, since sperm can survive for several days while the egg is viable for roughly 12–24 hours after release. Conceiving is most likely on the 2–3 days leading up to and including ovulation day.
Cycles vary from month to month, so treat this as a general estimate rather than a precise prediction — ovulation predictor kits or tracking basal body temperature can help narrow it down further.