Conception Calculator

Conception typically occurs during ovulation, about 14 days before the next period. From due date, we subtract 266 days (38 weeks). Since sperm can live 5 days and the egg 24 hours, the actual conception window spans several days.

Sperm can survive in the reproductive tract for up to 5 days, and the egg is viable for about 24 hours after ovulation. Intercourse anywhere in this 6-day window can result in conception, making the exact date uncertain.

Gestational age starts from the first day of your last menstrual period (LMP), about 2 weeks before conception. So at "2 weeks pregnant" conception hasn't occurred yet. Fetal age is actual time since conception, about 2 weeks less than gestational age.

Accuracy depends on cycle regularity. For regular 28-day cycles, accuracy is within a few days. Irregular cycles, stress, or late/early ovulation can shift actual conception. Ultrasound dating in the first trimester is most accurate.

The conception date range can help narrow down when conception occurred, but is not definitive proof of paternity. Given the 6-day fertile window and variation in cycle timing, DNA testing is the only certain way to determine paternity.