Answer: Hi From about two to three weeks of age, your baby will probably gain about 120-240 grams (four to eight ounces) per week until his or her birth weight doubles, usually by four to six months. In the first few days after birth, babies normally lose weight, then get back to their birth weight by about 10 days. In the first three months, a baby should gain, on average, 140 to 210 grams (five to 7½ ounces) per week. Between three and six months of age, the average rate of baby weight gain slows down to between 105 and 147 grams (four to five ounces) per week. breastfed babies grow more quickly in the first four to six months, and then slow down, while formula-fed babies grow more slowly at first and then gain weight faster, • Between six and 12 months, the average growth rate is 70 to 91 grams (2½ to three ounces) per week. • On average, babies double their birth weight by four or five months, and triple it by a year. parents should be aware that a baby’s birth weight depends more on the mother’s diet and health during pregnancy, than on genetics.