The average 5-month-old boy weighs about 16.6 pounds (7.5 kg), and the average 5-month-old girl weighs about 15.2 pounds (6.9 kg), based on the 50th percentile of WHO growth standards. But “average” is just the midpoint of a wide healthy range. A baby at the 15th percentile and a baby at the 85th percentile can both be growing perfectly well.
Healthy Weight Ranges at 5 Months
Growth charts plot children across percentiles, and the normal range stretches wider than most parents expect. For boys at 5 months, the 5th percentile sits around 13.4 pounds while the 95th percentile is roughly 20 pounds. For girls, that span runs from about 12.2 pounds at the 5th percentile to around 18.6 pounds at the 95th. A baby who consistently tracks along any percentile line within that range is following a healthy growth pattern.
What matters more than hitting a specific number is whether your baby’s weight follows a steady curve over time. A baby who has always been in the 20th percentile and stays there is doing exactly what they should. Pediatricians look at the trajectory, not a single snapshot.
The Birth Weight Doubling Milestone
You may have heard that babies should double their birth weight by 5 or 6 months. Research on 357 normal-weight infants found that the average baby actually hit that milestone earlier, at about 3.8 months (119 days). So by 5 months, most babies have already passed this benchmark. If your baby was born at 7 pounds, for example, you’d generally expect them to weigh at least 14 pounds by now.
Babies who were born smaller tend to double their birth weight sooner, while larger newborns may take a bit longer. The timing varies, but if your 5-month-old hasn’t yet doubled their birth weight, it’s worth mentioning at your next pediatric visit.
How Fast Weight Gain Slows Down
Weight gain isn’t constant throughout infancy. In the first few months, babies typically gain about 1 ounce (28 grams) per day. Around 4 months, that pace drops to roughly 20 grams per day. By 6 months, many babies gain 10 grams or less per day. This slowdown is completely normal and reflects a natural shift as babies become more active and their growth rate levels off.
This means that between 4 and 6 months, you can expect your baby to gain roughly 1 to 1.5 pounds per month, down from the 2 pounds per month pace of early infancy. Parents sometimes worry when weight gain seems to stall during this window, but the deceleration is a predictable part of development.
Breastfed vs. Formula-Fed Babies
How you feed your baby can affect where they fall on the growth chart. Breastfed infants typically put on weight more slowly than formula-fed infants during the first year. The difference becomes more noticeable after about 3 months, when formula-fed babies tend to gain weight more quickly. This gap persists even after solid foods are introduced.
This doesn’t mean breastfed babies are underweight. The WHO growth charts, which most pediatricians now use, were built primarily from data on breastfed infants and reflect their growth pattern as the biological norm. If your breastfed baby is tracking a lower percentile than a formula-fed baby of the same age, that’s expected rather than concerning.
How Much a 5-Month-Old Needs to Eat
At this age, babies need roughly 37 calories per pound of body weight per day (82 calories per kilogram). For a 16-pound baby, that works out to about 590 calories daily. In practical terms, a formula-fed baby at this weight would drink around 28 to 32 ounces of formula per day, split across five or six feedings, or roughly 5 ounces per bottle.
Breastfed babies are harder to measure by volume, but they generally feed 5 to 8 times per day at this age. Some 5-month-olds are starting to show interest in solid foods, though breast milk or formula still provides the vast majority of their nutrition at this stage.
When Weight Patterns Signal a Problem
Pediatricians use specific criteria to identify growth concerns. A weight below the 5th percentile for age, or a drop that crosses more than two major percentile lines on the growth chart, can indicate a problem sometimes called failure to thrive. A baby who falls from the 75th percentile to the 25th over a couple of months, for instance, would warrant investigation, even though the 25th percentile is perfectly normal on its own.
The key distinction is between a baby who has always tracked along a lower percentile and one whose growth is falling off their established curve. A baby who has consistently been at the 8th percentile may simply be small. A baby who was at the 50th percentile and drops to the 8th is telling a different story. Severity is measured in how far a baby’s weight deviates from the expected average: mild concern starts at roughly one standard deviation below the mean, moderate at two, and severe at three.
Adjusted Age for Premature Babies
If your baby was born early, their weight at 5 months of calendar age won’t match the numbers above, and it shouldn’t. Premature babies are assessed using corrected age, which subtracts the weeks of prematurity from their actual age. A baby born 8 weeks early who is now 5 months old would be compared to growth standards for a 3-month-old.
This correction makes a dramatic difference. Research shows that when premature babies are measured against their calendar age instead of their corrected age, their growth scores appear significantly lower, by as much as 4 to 5 standard deviations at early time points. For babies born very or extremely premature, age correction is recommended for all growth measurements through 36 months of corrected age. Without it, a perfectly healthy preemie can look severely underweight on paper.