Use of a fertility calculator does not increase the odds of conceiving a boy, according to HealthTap. Selection of sex of the embryo is essentially random and depends on whether the sperm that fertilizes the egg is carrying an X or a Y chromosome. The only way to ensure that the embryo is male is to use in vitro fertilization and preimplantation genetic diagnosis.
There is no functional or morphological difference between sperm carrying X or Y chromosomes, reports PubMed Central. The idea that there is a difference was raised by Dr. Shettles in the 1960s, but other researchers have proven that it is completely untrue.
The idea that using a fertility calculator to time intercourse in relationship to ovulation in order to preferentially conceive a boy or a girl was invented by Dr. Shettles, says BabyMed. The concept is based on the incorrect idea that sperm carrying Y chromosomes are faster but die more quickly than sperm carrying X chromosomes. Therefore, having sex on the day of ovulation was thought to be more likely to produce a boy because the faster Y chromosomes can get to the egg first. Having sex a day or two before ovulation favors producing a girl because the Y chromosomes die off before the egg arrives.