At 5 months old, the average baby boy weighs about 16.5 pounds (7.5 kg), and the average baby girl weighs about 15.2 pounds (6.9 kg). But “average” is just the midpoint on a wide spectrum of healthy weights. What matters more than hitting a specific number is whether your baby is growing steadily along their own curve.
Healthy Weight Ranges for 5-Month-Olds
The World Health Organization growth charts, which the CDC recommends for children under 2, show a broad range of normal weights at 5 months:
- Boys: 13.0 to 20.5 pounds (5.9 to 9.3 kg), with 16.5 pounds at the 50th percentile
- Girls: 11.9 to 19.2 pounds (5.4 to 8.7 kg), with 15.2 pounds at the 50th percentile
Those ranges represent the 5th through 95th percentiles, meaning 90% of healthy babies fall somewhere in between. A baby at the 15th percentile is just as healthy as one at the 80th percentile, as long as they’re following a consistent growth pattern over time. Your baby’s percentile at birth largely sets the track they’ll follow, and pediatricians expect them to stay in roughly the same range at each visit.
How Birth Weight Shapes the Number
A useful rule of thumb: most healthy, full-term babies double their birth weight by about 4 months. So by 5 months, your baby should weigh at least double what they weighed at birth, and likely a bit more. A baby born at 6.5 pounds might weigh around 14 to 15 pounds at 5 months. A baby born at 9 pounds could easily be 19 or 20 pounds and still be perfectly on track.
This is why comparing your baby’s weight to another baby the same age doesn’t tell you much. Genetics, birth size, and feeding patterns all play a role. The number on the scale only means something in the context of where your baby started.
How Fast Babies Gain Weight at This Age
Weight gain slows down noticeably around the 4- to 5-month mark. In the first few months of life, babies gain roughly 1 ounce per day. By 4 months, that drops to about 20 grams (just under ¾ of an ounce) per day. By 6 months, many babies are gaining 10 grams or less daily. So at 5 months, your baby is right in the middle of this slowdown, and gaining around 3 to 4 pounds per month is no longer expected. Something closer to 1 to 1.5 pounds per month is typical at this stage.
Parents sometimes worry when weight gain seems to stall compared to those rapid early months, but this deceleration is completely normal. It tends to coincide with babies becoming more active, rolling over, kicking more purposefully, and burning more energy throughout the day.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies follow slightly different weight trajectories, and the gap becomes more noticeable after about 3 months. Formula-fed babies typically gain weight faster from that point forward. Breastfed babies tend to put on weight more slowly through the first year, and this difference persists even after starting solid foods.
Neither pattern is better or worse. The WHO growth charts were developed using data from breastfed infants, so a breastfed baby tracking along the 30th percentile is doing exactly what’s expected. Problems only arise if a breastfed baby drops sharply across percentile lines, which would warrant the same attention regardless of feeding method.
What Growth Trends Actually Tell You
Pediatricians care far less about the specific number on the scale than about the trend over time. A baby who has been tracking along the 20th percentile since birth is growing perfectly. A baby who was at the 60th percentile at 2 months and has fallen to the 15th percentile by 5 months needs a closer look, even though the 15th percentile is technically “normal.”
The clinical concern is when a baby’s weight drops across two or more major growth percentile lines, or falls below the 3rd to 5th percentile. This pattern is sometimes called failure to thrive, and it can signal feeding difficulties, nutrient absorption problems, or other underlying issues. It’s not a diagnosis based on a single weigh-in. It requires a pattern of declining growth over multiple visits.
Signs of Healthy Growth Beyond the Scale
Weight is one measure of how your baby is doing, but it’s not the only one. At 5 months, a baby who’s growing well typically shows a cluster of physical and developmental signs that paint a fuller picture.
Your baby should be producing at least 6 wet diapers a day and having regular bowel movements. Physically, most 5-month-olds are raising their heads when lying on their stomachs, kicking and wiggling their arms and legs with purpose, and starting to roll over. Many can bear some weight on their legs when held upright. Hand-eye coordination is improving too: your baby is likely grasping at rattles, fingers, and anything else within reach, and pulling objects closer with a raking motion.
If your baby is alert, active, meeting these milestones, and feeding well, a number on the lower or higher end of the weight range is rarely a concern on its own. Growth is a pattern, not a snapshot, and the best way to track it is through regular well-baby visits where your pediatrician can plot your baby’s measurements over time and spot any changes in the trend early.