Conception occurs when a sperm cell fertilizes an egg, which typically happens within 12–24 hours after ovulation. However, pregnancy is established slightly later through implantation.
Here's the timeline: During ovulation, an egg is released from the ovary and enters the fallopian tube, where it remains viable for about 12–24 hours. If sperm are present in the reproductive tract during this window, fertilization can occur. The fertilized egg (now called a zygote) then travels down the fallopian tube over 3–4 days, dividing into multiple cells as it moves.
Implantation—when the developing embryo embeds into the uterine lining—typically occurs 6–10 days after ovulation. This is when pregnancy becomes established and hormonal changes begin that support the pregnancy.
It's important to note that sperm can survive in the female reproductive tract for up to 5 days, so conception can occur from intercourse that happened several days before ovulation, not just on the day of ovulation itself. This is why the "fertile window" is typically considered to be the 5 days before ovulation through the day of ovulation itself.
For practical purposes, when people say "conception," they may mean either fertilization (within 24 hours of ovulation) or implantation (6–10 days after ovulation), depending on context. Pregnancy tests detect the hormone hCG produced after implantation, so they won't show positive until roughly 8–14 days after ovulation.