The average weight of a four month old baby is between 4.93kg – 10.39kg. The weight of a four-month-old baby needs to be categorized into male and female, with the average male baby weighing between 5.25kg and 10.39kg; and a four-month-old female baby weighing between 4.93kg and 9.66kg. Babies begin to grow at a slightly slower rate in this period than in the first three months. Every baby grows and develops at a different rate, which is related to both congenital and acquired factors. Inborn factors mainly include intrauterine growth and development and genetic background, i.e. parents’ height. Acquired factors mainly include feeding style after birth, balanced nutrition, and the occurrence of diseases. As long as the weight of every four-month-old baby is within the normal range, there is no need to worry too much, and if there is any discomfort, it is recommended to consult a doctor in time.