At 5 months old, the average baby boy weighs about 16.5 pounds, and the average baby girl weighs about 15.2 pounds. But “average” is just the middle of a wide healthy range. Boys between roughly 13 and 20 pounds and girls between roughly 12 and 19 pounds all fall within normal growth curves. What matters more than hitting a specific number is whether your baby is gaining weight steadily along their own growth curve over time.
Average Weight at 5 Months
The World Health Organization growth charts, which pediatricians use at well-child visits, show these 50th percentile weights at 5 months:
- Boys: approximately 16.5 pounds (7.5 kg)
- Girls: approximately 15.2 pounds (6.9 kg)
The 50th percentile means half of healthy babies weigh more and half weigh less. A baby at the 15th percentile is not underweight any more than a baby at the 85th percentile is overweight. Both are normal as long as they’re following a consistent curve. A baby who has tracked along the 20th percentile since birth is growing exactly as expected, even though they weigh less than average.
How Much Weight Babies Gain Each Month
Between 4 and 6 months, babies typically gain 1 to 1.25 pounds per month. That’s noticeably slower than the rapid gains of the first three months, when many infants put on closer to 1.5 to 2 pounds monthly. This slowdown is completely normal and reflects a natural shift as your baby’s growth rate tapers from the explosive pace of early infancy.
A useful milestone to keep in mind: most healthy, full-term babies double their birth weight by about 4 months. So a baby born at 7.5 pounds would be expected to weigh around 15 pounds by 4 months and continue climbing from there. By 12 months, most babies will have tripled their birth weight.
Why Growth Curves Matter More Than a Single Number
Your pediatrician plots your baby’s weight on a growth chart at each visit, creating a line that shows their personal growth trajectory. The pattern of that line is far more informative than any single weigh-in. A baby who drops from the 60th percentile to the 20th percentile over two visits is more concerning than a baby who has always been at the 5th percentile.
Crossing two or more major percentile lines, either up or down, is what typically prompts a closer look. Small fluctuations between visits are common and can reflect something as simple as whether the baby just ate or had a wet diaper during the weigh-in. One data point rarely tells the full story.
Factors That Affect Your Baby’s Weight
Genetics plays the biggest role. Smaller parents tend to have smaller babies, and larger parents tend to have larger ones. A baby’s birth weight also sets the starting point for their growth curve. Beyond genetics, several other factors influence where your baby falls:
- Feeding method: Breastfed and formula-fed babies often follow slightly different growth patterns. Breastfed babies tend to gain weight faster in the first few months, then slow down relative to formula-fed babies in the second half of the first year. Both patterns are normal.
- Sex: Boys tend to weigh a pound or so more than girls at this age, which is why growth charts are sex-specific.
- Prematurity: Babies born early are assessed using their corrected age, not their calendar age, until they turn 2. A baby born 6 weeks early and now 5 months old would be evaluated against the growth standards for a 3.5-month-old.
How Feeding Supports Healthy Growth
At 5 months, breast milk or formula remains your baby’s primary source of nutrition. Breastfed babies at this age typically nurse about 6 to 7 times in 24 hours, though some feed more or less depending on their individual needs. Formula-fed babies generally eat every 3 to 4 hours, with most consuming somewhere around 24 to 32 ounces of formula per day.
Some families start introducing solid foods around this age, but solids at 5 months are more about exploration than calories. The bulk of your baby’s weight gain still comes from milk. If your baby seems hungry after finishing a bottle or nurses frequently and still seems unsatisfied, it may be worth discussing feeding volume with your pediatrician rather than assuming something is wrong.
Signs Your Baby May Not Be Gaining Enough
Occasional slow weeks happen. Illness, teething, or a growth plateau can temporarily affect weight gain. But certain patterns are worth paying attention to:
- Consistently flat or dropping weight curve across multiple visits
- Excessive sleepiness, including falling asleep during feedings before finishing
- Fewer than 5 to 6 wet diapers per day, which can signal inadequate intake
- Coughing, gagging, or arching the back during feedings, which may indicate a feeding difficulty
- Reduced social interaction, such as not mimicking facial expressions or seeming less engaged than expected for their age
These signs don’t automatically mean something serious. Many have straightforward explanations and solutions. But they’re worth bringing up with your pediatrician, especially if you notice more than one at the same time.
What “Too Heavy” Looks Like at 5 Months
Parents sometimes worry about a chubby baby, but at 5 months, a plump infant is rarely a concern. Babies are supposed to have fat reserves, and the rolls and round cheeks that come with healthy weight gain in infancy don’t predict later obesity. Pediatricians almost never recommend restricting a baby’s milk intake at this age. If your baby is consistently above the 95th percentile, your doctor may simply monitor the trend over time to make sure growth doesn’t accelerate disproportionately to length.