Ovulation Calculator – Fertile Window and Conception Days
Estimate your ovulation date and fertile window for conception planning. Enter the first day of your last period and average cycle length. The calculator uses the luteal phase (14 days before next period) to predict ovulation and shows your 6-day fertile window. Pair with our pregnancy due date calculator for full planning.
Ovulation Calculator
Estimate your ovulation date and fertile window. Enter the first day of your last period and average cycle length. The fertile window spans 6 days—5 before ovulation plus the day of ovulation.
How the ovulation calculator works
The luteal phase (time from ovulation to next period) is more consistent than the follicular phase. It averages about 14 days:
Ovulation date = Last period + (Cycle length − 14 days)
Fertile window = 5 days before ovulation through ovulation day. Sperm can live up to 5 days; the egg survives 12–24 hours after release. Best conception odds: 1–2 days before ovulation.
Understanding ovulation and conception planning
Ovulation is when a mature egg is released from the ovary. It occurs once per cycle, typically around the midpoint. The fertile window includes the days when sperm could meet the egg—sperm survive several days, so intercourse before ovulation can still result in conception. Tracking your cycle helps identify your most fertile days.
For irregular cycles, the calendar method is less accurate. Consider ovulation predictor kits (OPKs) or basal body temperature tracking for better precision. After conception, use the pregnancy due date calculator to estimate when your baby might arrive. This tool is for educational use; discuss fertility with a healthcare provider as needed.