When does implantation happen and when can I take a pregnancy test?

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Accepted Answer

Implantation is the process by which the fertilized embryo embeds into the uterine lining after ovulation. According to Wilcox et al. 1999 NEJM, about 84% of normal pregnancies implant 8–10 days post-ovulation, with day 9 most common; implantation after day 12 carries a higher risk of early miscarriage. About 25% of women experience light spotting (implantation bleeding) around this time, and absence of any symptoms is also normal. Once implantation begins, βhCG is produced and doubles every 24–48 hours; home urine pregnancy tests typically turn positive from 12–14 days post-ovulation (around the expected period date). Testing too early can give a false negative, so testing 1–2 days after a missed period is more accurate. This calculator marks the average implantation window and recommended test timing based on ovulation date or LMP as a reference; for a definitive diagnosis, see an obstetrician for serum βhCG and ultrasound.