Implantation timing, explained

What the 1999 study measured

Wilcox, Baird and Weinberg dated implantation by collecting daily urine samples and identifying the first day chorionic gonadotropin appeared. Implantation occurred 6 to 12 days after ovulation, and 84 percent of pregnancies implanted on day 8, 9 or 10. That is a hormone measurement in a research setting, not something anyone perceived, and the paper reports nothing about symptoms. This site does not carry a list of implantation signs, because the study that dated implantation did not find any.

Days past ovulation are counted from an estimate

DPO counts forward from the day of ovulation, so everything downstream depends on that day being right - and unless it was confirmed by testing or monitoring, it was calculated. This site estimates ovulation by counting back from the next expected period rather than forward to a fixed day 14, because Bull 2019 found the follicular phase is what varies most. Even so, the luteal phase itself had a 95 percent interval of 7 to 17 days in that dataset, which puts a band of several days around any estimated ovulation date. A window of dates is the honest output; a single date is not.

What this page deliberately does not contain

No symptom list, as above. No earliest test date either: chorionic gonadotropin only begins rising once implantation starts, so a test before then has nothing to detect, and after that the answer depends on the sensitivity of the specific test and on how fast the level climbs. Home test sensitivities differ enough that a date printed here would be misleading for a large share of readers. There is also no implantation dip, no probability of success, and no interpretation of any of it - those are clinical readings, and the tool this page ends at carries no ads for the same reason.

What the numbers after implantation mean

Once hCG is detectable, the arithmetic that follows is a doubling time - division and a logarithm, applied to two values and the hours between them. The published reference point is Barnhart 2004, which observed, in symptomatic women who went on to have a viable intrauterine pregnancy, a slowest rise of 24 percent over one day and 53 percent over two. Those figures replaced an older teaching of 66 percent in 48 hours, and the authors' conclusion was that intervention should be more conservative rather than less. A doubling time is arithmetic, not a prognosis, and this site presents it as one.

Official sources

• Wilcox, Baird & Weinberg, Time of implantation of the conceptus and loss of pregnancy, N Engl J Med 1999
• Bull et al., Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles, npj Digital Medicine 2019
• ACOG, Fertility Awareness-Based Methods of Family Planning (patient FAQ)
• Barnhart et al., Symptomatic patients with an early viable intrauterine pregnancy: HCG curves redefined, Obstet Gynecol 2004

Frequently asked questions