Most 10-month-old boys weigh between 17.5 and 22 pounds, and most girls weigh between 16 and 20.5 pounds, based on the WHO growth standards used by pediatricians in the United States. But a single number matters far less than your baby’s growth trend over time. A baby who has consistently tracked along the 15th percentile is growing just as well as one tracking the 85th.
Average Weight by Sex
The CDC and American Academy of Pediatrics recommend using the WHO child growth standards for all children from birth to age 2, regardless of whether they’re breastfed or formula-fed. Those standards place the 50th percentile (the statistical middle) for a 10-month-old boy at roughly 20 pounds and for a girl at about 18.5 pounds. The healthy range stretches well above and below those midpoints. A boy at the 5th percentile weighs around 16.5 pounds, while one at the 95th percentile is closer to 24 pounds. For girls, the 5th percentile sits near 15 pounds and the 95th near 22.5 pounds.
These percentiles describe a population, not an individual baby. Your pediatrician plots your child’s weight at every visit specifically to watch the curve, not to compare one child against another.
Growth Rate at This Age
Between 9 and 12 months, babies typically gain 2 to 4 ounces per week. That’s noticeably slower than the rapid gains of the first few months, and it catches many parents off guard. The slowdown is normal. Babies are burning more energy now because they’re crawling, pulling up, and cruising along furniture.
That increased movement has real metabolic effects. Crawling raises energy expenditure and can reduce fat mass, which means some babies look leaner even as they continue to grow. Research tracking children long-term found that babies who crawled before walking had lower body fat percentages years later, suggesting this stage of physical activity shapes body composition in lasting ways.
Breastfed vs. Formula-Fed Babies
If your baby is breastfed and seems lighter than formula-fed peers, that’s a well-documented pattern rather than a problem. Formula-fed infants gain more weight relative to their length during the first year. By 9 to 12 months, formula-fed babies carry roughly 300 grams (about two-thirds of a pound) more lean mass than breastfed babies, though fat mass is similar between the two groups. The difference shows up mostly in the speed of weight gain through about 7 months and then levels off somewhat.
Because the WHO growth charts were built from data on breastfed infants, they reflect that slightly leaner growth pattern. A breastfed baby tracking along the 30th percentile on the WHO chart is right where expected.
What Your Baby Needs to Eat
At 10 months, your baby needs roughly 750 to 900 calories per day. About 400 to 500 of those calories should still come from breast milk or formula, which works out to around 24 ounces a day. The rest comes from solid foods: soft fruits, vegetables, grains, and protein sources like small pieces of meat, beans, or egg.
Many parents worry when their baby starts refusing a bottle or nursing session as solid food intake climbs. As long as total calorie intake stays in range and your baby is gaining steadily, a gradual shift toward more solids and less milk is exactly what’s supposed to happen at this age.
When a Weight Trend Is Concerning
Pediatricians look for specific red flags rather than fixating on a single percentile number. The clinical criteria that raise concern include: weight below the 5th percentile for age, a drop that crosses two or more major percentile lines on the growth chart, or any actual weight loss between visits. A baby who has always been small but tracks a consistent curve is generally fine. A baby who was at the 60th percentile and slides to the 15th over two or three visits needs closer evaluation.
The distinction matters. A child who has always trended in a lower percentile range may simply be meeting their genetic growth potential. A sudden decline suggests something has changed, whether it’s a feeding difficulty, an illness, or an absorption issue, and warrants investigation.
Premature Babies Need Adjusted Age
If your baby was born early, their weight should be compared against their corrected age, not their calendar age. Corrected age is calculated by subtracting the number of weeks of prematurity from the baby’s actual age. So a 10-month-old born 6 weeks early would be plotted on growth charts as an 8.5-month-old.
This adjustment is especially important for babies born very early (before 32 weeks). Research confirms that skipping the correction leads to frequent misclassification of healthy preterm babies as underweight. Current evidence supports using corrected age for all growth assessments through at least 36 months of corrected age for extremely and very preterm children. Your pediatrician should be making this adjustment automatically, but it’s worth confirming if you’re comparing your baby’s weight to online charts at home.
What Actually Determines Your Baby’s Size
Genetics is the biggest factor. Tall, lean parents tend to have tall, lean babies. Shorter, stockier parents tend to have stockier babies. By 10 months, many children are starting to settle into their genetically programmed growth channel after the rapid, somewhat unpredictable gains of early infancy.
Beyond genetics, the variables that influence weight at this age include feeding method (as described above), caloric intake from solids, activity level, sleep quality, and whether the baby has been sick recently. A stomach virus or ear infection can easily flatten weight gain for a week or two, and most babies bounce back quickly once they recover. Chronic or repeated illnesses have a larger cumulative effect and are one of the things pediatricians watch for when a growth curve starts to falter.