Understanding the implantation window
Implantation — when a fertilized egg attaches to the uterine lining — is a key early milestone in pregnancy, and the moment hCG production begins. Research tracking implantation timing across many cycles has found it typically occurs in a window roughly 6 to 10 days after ovulation, rather than on a single universal day.
Why symptoms aren't a reliable signal
Light spotting and mild cramping are sometimes attributed to implantation, but both overlap substantially with normal premenstrual symptoms that have nothing to do with pregnancy. Relying on symptom-watching to determine pregnancy status is considerably less reliable than a properly timed pregnancy test.
Connecting implantation to test timing
Because hCG only starts being produced after implantation, and needs several days to reach a reliably detectable level, the implantation window itself is generally too early to test — which is why pregnancy tests are recommended closer to the day of a missed period rather than immediately after the estimated implantation window.