At what age does an infant’s birth weight triple?

• Average weights
• By age
• What to expect
• What affects baby weight?
• Summary

It is common for babies to lose around 10% of their weight shortly after birth. This decrease is mostly due to fluid loss and usually nothing to worry about. Most babies gain back this weight within 1 week.

Weight charts can help a person tell what percentile their baby’s weight falls into. For example, if their weight is in the 60th percentile, it means that 40% of babies of the same age and sex weigh more, and 60% of these babies weigh less.

This does not necessarily mean that any baby weighs too much or too little. It can simply indicate where a baby’s weight falls on a spectrum.

The chart below shows baby weights in the 50th percentile. This is the average weight. Male babies tend to weigh a little more than female babies, so the chart is divided by sex.

Babies grow and gain weight the fastest within the first 6 months of life. Although this can vary, babies tend to gain around 4–7 oz, or 113–200 grams (g), per week in the first 4–6 months.

Weight gain then slows slightly, with an average gain of around 3–5 oz (about 85–140 g) per week when the baby is 6–18 months. On average, babies triple their birth weight by their first birthday.

Growth patterns do not follow a clear schedule, however.

Some babies gain weight steadily and stay in the same percentile, or close to it, for several months. Others gain weight rapidly, signalling a growth spurt, which can happen at any time. This may move a baby into a new weight percentile.

It is important not to focus on weight as the only indicator of physical development. Other measurements of this development include the baby’s length and head circumference.

Considering all three measurements gives doctors an idea about how the baby is growing, compared with other babies of the same age and sex.

Meanwhile, it is also important to keep other developmental milestones in mind. Various checklists of milestones by age are available, including one from Pathways.org, which is endorsed by organizations such as the American Academy of Pediatrics and the National Association of Pediatric Nurse Practitioners.

For anyone looking for more information about what influences the weight of a baby, several factors can be involved, including:

Sex

Male newborns tend to be bigger than female newborns, and they typically gain weight a little faster during infancy.

Nutrition

Weight gain and growth rates can also depend on whether the baby consumes breast milk or formula.

The American Academy of Pediatrics notes that breastfed babies gain weight and grow faster than formula-fed babies during the first 6 months.

However, that rate can shift during the next 6 months. Breastfed babies may gain weight and grow more slowly than formula-fed babies when they are aged 6 months to 1 year.

Medical conditions

Underlying health issues can cause a baby to gain weight more slowly. For example, babies with congenital heart irregularities may gain weight at a slower rate than babies without this condition.

Health issues that affect nutrient absorption or digestion, such as celiac disease, may also lead to slow weight gain.

Prematurity

Babies born prematurely may grow and gain weight more slowly during their first year than babies born at full term.

However, many babies born prematurely gain weight rapidly and “catch up” by about their first birthday.

The average birth weight for full-term male babies is 7 lb 6 oz, or 3.3 kg. For female babies born full-term, the average birth weight is 7 lb 2 oz, or 3.2 kg.

Baby weight charts can help a healthcare team track a baby’s physical development by comparing the baby’s weight with the weights of others of the same age and sex.

Still, a doctor usually looks for steady growth, rather than a target percentile, when assessing a baby’s physical development. And even if a baby’s weight is in a lower percentile, they will not necessarily be a small adult — just as longer babies do not necessarily become tall adults.

Knowing about average weights by month can help people gauge their babies’ physical development, but doctors also look for other important indicators, such as length and head circumference.

Healthcare professionals also take into account whether a baby is generally hitting other milestones on time. And by taking a detailed medical history, they can rule out any medical conditions or nutritional considerations that may be preventing a baby from gaining weight appropriately.

Last medically reviewed on September 6, 2021

• Pediatrics / Children's Health
• Pregnancy / Obstetrics
• Parenthood

Babies typically lose weight after birth, before they start to gain. A generally accepted rule of thumb is that a baby can be expected to lose about 3–7 percent of their birth weight during the first 5 days after birth. Parents should expect their baby to return to his or her birth weight by about day 10. 

Many babies double their birth weight by age 4 to 6 months and triple their birth weight by their first birthday. But babies who gain more slowly or more quickly may be perfectly healthy too. Your baby's doctor will monitor your baby's growth over time (weight, length, and head circumference) to ensure that they're getting all of the calories and nutrients they need. This is one reason why it's recommended babies have at least 6 doctor's visits during the first year.

Babies’ weight gain and loss doesn’t follow a pattern

It’s not clear how much weight exclusively breastfed babies lose and then gain in their first 14 days. A recent study of weight change in nearly 150,000 healthy babies found that it’s not uncommon for newborns to be below their birth weight even 21 days after delivery.

What are signs my baby is eating enough? 

Parents’ concern over weight is easy to understand given that it’s the only reliable indicator of growth. But if you know the signs that your baby is getting enough to eat, you don’t need an expensive in-home baby scale. A well-fed baby will… 

• be active and alert 
  
• be satisfied after breastfeeding 
  
• breastfeed at least 8–12 times during each 24-hour period 
  
• by day 3, have three or more poops a day
  
• by day 5, have yellow poop
  
• by day 5, have clear or pale yellow pee and six or more wet diapers a day
  

After 4 weeks of age, some babies continue to poop after every feeding, while others poop only once every other day, or once every 3–5 days. (Click here for more scoop on poop.) 

As long as you see these indicators of good health, there’s generally no reason to worry about having your baby’s weight measured between well-child visits.

What if my baby suddenly stops gaining weight? 

As long as your baby is reaching her developmental targets and isn’t losing weight, there’s no need to worry about a pause in weight gain. Children who fail to gain enough weight in the first 9 months will usually catch up over time. So parents seldom need to increase their child’s calories (by supplementing with donor milk or artificial infant formula). Consuming too many calories in infancy can actually lead to weight problems later in life. 

But if your baby loses more than 7 percent of their birth weight or gains weight slowly in the early days and weeks following their birth, your baby’s health care provider may ask you to bring them in for weight checks. A review of your breastfeeding routine and periodic weight checks will ensure that they're getting enough to eat and that there are no underlying health issues.

Does weight really matter? 

Weight is a measure of nutrition. When babies get too little food, too much food, or the wrong type of food, they can become malnourished. Today, experts agree that a brief period of underfeeding (days versus weeks or months) is unlikely to cause permanent damage. It can, however, have serious short-term consequences. Timing seems to be the key factor, since even a brief period of underfeeding in the first days after birth can lead to hyperbilirubinemia (jaundice) and hypoglycemia (low blood sugar). And if you’re concerned about your baby’s growth or feeding, contact their pediatrician.