Many factors affect infant weight gain including illness, metabolism, body shape, feeding methods and personality. Your baby's doctor will likely use a Centers for Disease Control growth chart to assess your infant's weight.
Babies may drop between 5 and 10 percent of original weight after birth. Within two weeks, most infants gain the weight back. At one month, average baby weight is between 6.6 to 11.2 lbs. At three months, normal baby weight ranges from 9.5 to 15.4 lbs.
Babies should gain 1 to 2 lbs. monthly the first six months. Weight should range from 11 to 17.6 lbs. at four months and 13.6 to 21.1 lbs. by six.
The Centers for Disease Control suggests a range of 15.6 to 24 lbs. for 9-month-old infants. Growth rate averages about 1 lb. per month the first year.
By 12 months old, a baby should weigh 17.6 to 26.6 lbs. Formula-fed babies will have gained, on average, 1 lb. more than their breast-fed peers the first year.
An active baby will likely gain at a slower rate than her more laid-back counterpart. By 18 months old, babies should weigh between 20 and 30.6 lbs.
By 24 months of age, normal baby weight is 22 to 34.1 lbs. and should represent nearly four times his birth weight.