Question: how much weight should my baby gain by 4 months?
Answer: By 4 months, many babies have doubled their birth weight. This month, babies gain about 1 to 1¼ pounds (560 grams) and about 0.8 inches (2 centimeters) in length. Since your child's birth, the doctor has been recording growth in weight, length, and head size (circumference) during your regular well-baby visits.