The standard weight of a 4-month-old baby is about 6.5kg, but there are individual differences. The weight standard for 3-12 months old babies is calculated by using the formula weight = (age in months + 9)/2kg, and the calculated standard weight for 4 months old babies is 6.5kg. If the weight is not up to standard, below two standard deviations or less, we should actively look for the cause to see if it is caused by insufficient feeding or related diseases, and give appropriate treatment. If the weight is overweight, more than two standard deviations, you need to avoid overfeeding, and if necessary, go to the hospital to see if there is any other disease causing the problem. Childhood obesity can cause cardiovascular disease, diabetes and other problems in adulthood, which need to be taken seriously. Baby’s weight gain is not a uniform increase, each baby’s weight gain varies, and is easily affected by factors such as feeding, nutritional status, and whether or not they are often sick. It is recommended to have regular medical checkups at the Child Health Unit to understand the dynamic changes in your baby’s weight.