How Much Should a 9-Month-Old Weigh?

Ultimate Q&A

how-much-should-a-nine-month-old-weigh

Image: Mason Masteka

There’s a wide range of healthy sizes and weights for infants and young children.

Pediatricians use height and weight charts to track your child’s physical growth and development at each appointment. These charts use percentile curves to make sure that your baby is at a healthy size and weight relative to their previous growth.

Charting your baby's weight

Of course, your child’s weight will not stay the same, but it should remain relatively predictable and follow a general trend: you should be able to trace a smooth line along your baby’s growth chart as he gets older. The percentile isn’t as important as the fact that your baby is growing consistently overall. A baby in the 30th percentile for height and weight is likely to be just as healthy as a baby in the 80th percentile.

If your baby fails to gain weight as he grows older, that might indicate a problem: maybe he’s not eating enough, or he might have a developmental delay. Your pediatrician will continue to monitor your child’s growth.

It doesn’t necessarily mean that something’s wrong if your baby stops gaining weight, or even loses a little bit of weight. It’s scary when you sense that something is wrong with your child’s development, but there are lots of possible reasons for an infant to temporarily lose weight, or gain weight less quickly than they had been.

About weight gain in babies

Between six months and twelve months of age, babies will naturally gain weight more slowly than they did in the first six months. A child who is fighting off an illness may eat less than he does with he is healthy. You and your doctor should pay attention to the overall growth curve; as long as your baby is getting enough nutrition and retaining a healthy size and weight over several months, he’s probably healthy and developing well.

​Many parents are concerned about children not gaining enough weight, which can result in a condition called “failure to thrive.” Failure to thrive simply means that your child is not growing as much as he or she should be.

There are many possible causes, ranging from poor nutrition to a possible food allergy or intolerance, or a medical condition like cystic fibrosis. It’s always important to check in with your pediatrician regularly during the first year of your baby’s life so that any possible problems can be diagnosed and treated as soon as possible.

9 month old

Image: J.K. Califf

The importance of diet​

It’s also possible for a baby to weigh too much. Infants in the 95th percentile or higher for weight may be at risk for childhood obesity

As with adults, a baby’s diet and the ability to move freely and often impacts their physical development and healthy weight. It’s important to offer your baby healthy food choices as they begin to transition to solid foods in addition to breast milk or bottled formula.

Limit fruit juices, processed foods, and added sugars. Instead, try to encourage your baby to eat lots of vegetables and whole grains, and model such healthy eating yourself. This is especially important if you’re breastfeeding, as your nutrition will affect the quality of the milk you give your baby.​

Your baby needs exercise to develop their muscles and maintain a healthy weight. This doesn’t mean that an infant needs to go to the gym or work out of course, but it’s important to let your child crawl around, move their arms and legs freely, reach and grab for toys.

What's normal

At nine months old, your baby might attempt to pull up on furniture, stand, or even begin walking. Pediatricians recommend “tummy time” for every baby. As your child grows stronger, continued tummy time will let them build their muscles and gross motor skills. Even more important is to try not to restrict your child’s movement by letting them spend too many hours in car seats, bouncy chairs, or swings. Let them move on their own as much as possible.​


Obviously, how much your child weighs at nine months will be strongly impacted by how much he weighed at birth. The range of healthy weight for children will begin to narrow as they grow. But at nine months old, the range is still very wide, and the healthy weight for your child will depend on their previous development. Infants should triple their birth weight by the time they are a year old. A nine-month-old baby commonly weighs between 16 and 21 pounds, with boys typically weighing more than girls at the same age.​

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