The Short Answer
Implantation typically occurs 6–12 days after ovulation, with the most common window being 8–10 days post-ovulation (DPO). Since sperm can survive up to 5 days in the reproductive tract, sex that happened 1–5 days before ovulation could result in implantation 7–17 days later.
The Egg Is Released
The mature egg bursts from its follicle on the ovary and enters the fallopian tube. It’s viable for only 12–24 hours. If sperm are already present (from intercourse in the previous 1–5 days) or arrive within this window, fertilization can occur.
Sperm Meets Egg
Of the ~200–300 million sperm released, only about 200 reach the egg in the fallopian tube. One penetrates the outer layer (zona pellucida), and the genetic material from both parents combines. The fertilized egg (zygote) begins dividing almost immediately.
The First Cell Divisions
The zygote divides: 2 cells, then 4, then 8. It’s still in the fallopian tube, slowly traveling toward the uterus. Each cell at this stage is totipotent — capable of becoming any cell type in the body.
A Solid Ball of Cells
At about 16–32 cells, the embryo is called a morula (Latin for “mulberry” — that’s what it looks like). It enters the uterine cavity around day 4 but is still free-floating, not yet attached to anything.
Ready for Implantation
The morula develops into a blastocyst: a hollow sphere with an inner cell mass (future baby) and an outer layer of trophoblast cells (future placenta). At around 200–300 cells, the blastocyst “hatches” from its protective shell (zona pellucida) — a necessary step before it can attach to the uterine wall.
Burrowing In
The trophoblast cells attach to the uterine lining (endometrium) and begin burrowing into it. This process takes 1–3 days to complete. The most common implantation day is 9 DPO, but the full window spans 6–12 DPO. Once implanted, the embryo begins producing hCG — the hormone that pregnancy tests detect. Detectable hCG levels typically appear 1–2 days after implantation.
When to Test
Since hCG production begins 1–2 days after implantation, and most implantation occurs at 8–10 DPO, the earliest you can reasonably test is 10–11 DPO. At 12–14 DPO, most tests will give a definitive answer.