Conception Date Calculator
Knowing your approximate conception date helps understand your pregnancy timeline. This calculator estimates when conception occurred based on either your last menstrual period (LMP) or your due date, adjusted for your individual cycle length.
Conception typically occurs around ovulation, which happens approximately 14 days before the start of the next period (the luteal phase). For a standard 28-day cycle, ovulation is around day 14; for a 35-day cycle, around day 21. This calculator adjusts the ovulation estimate based on your cycle length, since the luteal phase is relatively consistent at about 14 days while the follicular phase varies.
The fertile window spans approximately 5 days before ovulation through 1 day after. Sperm can survive in the reproductive tract for 3–5 days, while the egg is viable for 12–24 hours after release. This means intercourse several days before ovulation can result in conception. When calculating from a due date, the calculator subtracts 266 days (the average time from conception to birth) adjusted for your cycle length.
These calculations provide estimates based on averages. Actual conception timing can vary even with regular cycles. Ultrasound dating in the first trimester is the most accurate way to determine gestational age. Consult your healthcare provider for definitive dating.