When Does the Average Newborn Double His Weight?

Newborns gain weight rapidly during the first 6 to 12 months of life. Most babies double their birth weight by 6 months of age. Although growth rate slows after 6 months, babies continue steadily gaining weight in their first year of life. However, growth rate is dependant upon a number of factors, especially whether the child is breastfed or formula-fed.

Newborn Ups and Downs

Most full term newborn babies, born between 38 and 40 weeks gestation, weigh between six and nine pounds at birth. During the first week of life, babies tend to lose some weight, but the lost weight is usually regained by the second week of life. Formula fed babies tend to lose about five percent of their birth weight in the first week; whereas, breastfed babies can lose between seven and 10 percent of their birth weight in the first week, notes the American Pregnancy Association.

Four to Six Months

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How Much Weight Do Newborns Gain?

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Newborns continue to gain about five to seven ounces a week for the first 3 to 4 months of life. Most babies should have doubled their birth weight by 6 months, but many may have doubled their birth weight by 4 months of age. By 1 year old, most babies have tripled their birth weight. The rate at which your baby gains weight is dependent on a number of factors, such as if the child was premature, has been sick, your child’s sex or if your child is breastfed or formula-fed.

Breastfed and Formula-Fed Differences

At about 4 months of age, growth rates between breastfed and formula-fed babies start to change and are often physically noticeable. Because breast milk has a different effect on the baby's metabolism and insulin levels, breastfed babies tend to store fat differently. Thus, breastfed babies tend to be longer and leaner, and weigh about a pound less than formula-fed babies at 12 months old, according the Ask Dr. Sears website.

Breastfeeding and Weight Gain

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How to Calculate Percentile Weight Loss for Infants

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In addition to breastfed babies being lean, they are also less likely to become obese later in life, notes Doraine Bailey, MA, IBCLC. Breastfed babies are in more control on the amount of milk they drink and less likely to over-consume. This teaches them to stop eating when they are full, instead of continuing to eat until the bottle is empty. When infants continually consume more than necessary, they gain more weight, and this habit can continue into adulthood. Furthermore, breast milk contains many different flavors based on what the mother eats; whereas, formula milk always taste the same. Consequently, breastfed babies are more open to eating a wider variety of foods, such as fruits and vegetables than formula-fed babies.