This calculator shows possible implantation dates based on when you ovulated (either actual, or calculated based on last period): that is, approximately when your egg, if successfully fertilized, would attach to the endometrium, after which the pregnancy hormone is produced and starts to double quickly.
From Fertilization to Implantation
During the first phase of the menstrual cycle, the Follicular Phase, follicles start to develop in one of the ovaries, stiumulated by the hormone FSH, courtesy of the pituitary gland. At some point, one follicle becomes dominant, probably having had enough of life behind ovary walls, and, with help from a surge of LH, breaks out of the ovary (ie. ovulation).
Now alone out in the fallopian tube, she waits. And waits... With good-timing, and a little/lotta baby dust, if just one of hundreds of millions of sperm manages to find its way and fertilizes the egg, a zygote comes to fruition.
Over the next 5 to 6 days, the newlyweds have two primary tasks: move from the oviduct into the uterus; And, during this journey, transform from the 1-celled fused zygote to a multi-celled blatocyst which can implant into the uterine wall. All this, and more, as we go through our day, wondering if it's time to stock up on pregnancy tests...!
From Implantation to Pregnancy Testing
As soon as implantation occurs, hCG production begins which immediately alerts the corpus luteum (the leftover follicle which ovulated the egg) that it should emit progesterone, which, in turn, sustains the uterine lining so that menstruation does not occur. By doing this, hCG, often referred to as the pregnancy hormone, plays a crucial role in early pregnancy, since the placenta can not yet produce sufficient quantities of progesterone. hCG also sends a signal to its fellow hormone FSH: do not, repeat, NOT, stimulate any more follicles until further notice - we're pregnant!
And, of course, hCG is what both qualitative and quantative pregnancy tests detect. A qualitative test, such as home pregnancy tests, basically indicates yes/+/positive (pregnant) if the level of hCG in the sample is greater than or equal to the level measured by the test, or no/-/negative (not pregnant) if you are either not pregnant, or, as can happen if you test too early, the hCG level in your urine is less than the level detected by the test. By contrast, a quantitative blood test, which your doctor may order, can show exactly how much hCG is actually in the bloodstream.
hCG doubles rapidly - typically every 48 to 72 hours in the first trimester of pregnancy, after which it declines somewhat and then stays at the new plateau during trimesters 2 and 3.
Related Pregnancy Calculators and More
Simulates pregnancy hormone doubling based on the most likely implantation dates in your cycle, and, using 2 and 3 day doubling, shows what levels would be on/before/after the day of your next period.
Calculate when to take a pregnancy test based on your menstrual cycle info. Also helpful if you want to early pregnancy test.
How HPTs work, taking the test, false negatives and positives, accuracy rate and more.
Track and chart your fertility cycles for free, including BBT charting. Includes supportive TTC charting community, dozens of conceiving calculators, period tracker, pregnancy tracker - online and mobile.