The time during which the embryo or fetus gets fully developed in the uterus is called the gestation period or pregnancy. But in the case of gestation period for humans, the accurate time of ovulation and therefore the time of fertilization is hard to determine.hus, the gestation period for humans in days can be calculated as 280 days. However, the actual gestation period, as compared to other mammals, is around 267 days. But then what is the average gestation period for humans? It is taken to be about 259 to 294 days.