The average weight of a 5-month-old baby is about 15.2 pounds (6.9 kg) for girls and 16.5 pounds (7.5 kg) for boys, based on the World Health Organization growth standards. A healthy range is broad, though. Boys between the 3rd and 97th percentiles weigh anywhere from about 13.2 to 20.3 pounds, and girls from about 12.1 to 19.2 pounds.
What the WHO Growth Charts Show
Both the American Academy of Pediatrics and the CDC recommend using WHO growth charts to assess weight during the first two years of life. These charts are built from data on healthy, breastfed infants across multiple countries, making them the gold standard for tracking early growth.
At 5 months, the 50th percentile (the true statistical middle) falls at roughly 16.5 pounds for boys and 15.2 pounds for girls. But “average” is less important than your baby’s individual curve. A baby who has tracked along the 20th percentile since birth is growing normally, even though they weigh less than most babies their age. What matters is that the trajectory stays consistent over time, not that it lands on a specific number.
How Percentiles Work
A percentile ranks your baby against a reference population. If your 5-month-old is at the 25th percentile for weight, that means they weigh the same as or more than 25% of babies their age and less than 75%. Being at the 10th percentile doesn’t mean something is wrong, just as being at the 90th doesn’t automatically mean a baby is overfed. Pediatricians look at whether a baby’s percentile stays relatively stable from visit to visit. A sudden jump from the 60th to the 15th percentile is more concerning than consistently tracking at the 15th.
Typical Weight Gain at This Age
Weight gain slows noticeably around the 4- to 5-month mark. In the first few months of life, babies gain roughly 1 ounce (28 grams) per day. By 4 months, that rate drops to about 20 grams per day, and by 6 months many babies are gaining 10 grams or less daily. This slowdown is completely normal and reflects a shift toward more active movement, rolling, and muscle development rather than rapid fat accumulation.
A common milestone to watch for: most healthy, full-term babies double their birth weight by about 4 months. If your baby weighed 7.5 pounds at birth, you’d expect them to be around 15 pounds or a bit more by 5 months. Tripling birth weight typically happens closer to the first birthday.
Breastfed vs. Formula-Fed Babies
Feeding method affects weight gain patterns, and this becomes more noticeable right around the 5-month mark. Breastfed babies typically put on weight more slowly than formula-fed babies during the first year. Formula-fed infants tend to gain weight more quickly after about 3 months, and these differences persist even after solid foods are introduced.
This means a breastfed 5-month-old who is a bit lighter than the chart’s 50th percentile may be growing perfectly well. The WHO charts already account for breastfeeding patterns, which is one reason they’re preferred over older growth references for this age group.
Signs of Healthy Growth Beyond the Scale
Weight is one piece of the picture, but it’s not the only one. At 5 months, healthy growth also looks like a baby who is alert and interested in their surroundings, producing at least six wet diapers a day, and hitting physical milestones like reaching for objects, holding their head steady, and starting to roll over. Steady gains in length and head circumference alongside weight give a fuller sense of overall development.
When Weight Gain May Be Too Slow
For babies between 3 and 6 months old, gaining less than about 0.67 ounces per day is a threshold that can signal a problem. Other red flags include a baby who suddenly stops growing after following a steady curve, seems unusually sleepy or disinterested in their surroundings, cries frequently, or falls behind on physical milestones like rolling over.
Sometimes slow weight gain is simply a matter of calorie intake, especially if a breastfed baby isn’t transferring milk efficiently or a feeding schedule needs adjustment. Other times it reflects an underlying health issue. The pattern over time tells the story more than any single weigh-in.
Premature Babies and Corrected Age
If your baby was born early, their weight should be assessed using corrected age, not their actual age. Corrected age subtracts the weeks of prematurity from their calendar age. A baby born 8 weeks early who is now 5 months old has a corrected age of about 3 months, and their weight is compared to the growth chart at 3 months instead. In clinical examples, a premature infant at 5 months actual age with a corrected age of 3 months might weigh around 10.6 pounds (4.8 kg), which looks low for 5 months but falls within a normal range for 3 months.
Most premature babies gradually catch up to their full-term peers, often by age 2, but using corrected age in the meantime prevents unnecessary worry about weight that is actually right on track for their developmental stage.