Most 5-month-old babies weigh between 12 and 18 pounds, depending on sex and birth size. Boys at this age typically weigh around 16.5 pounds on average, while girls average closer to 15 pounds. But the number on the scale matters far less than whether your baby is following a consistent growth curve over time.
Average Weight at 5 Months
The World Health Organization growth standards, which pediatricians in the U.S. use for children under two, show a wide range of healthy weights at five months. For boys, the 50th percentile (the midpoint) falls around 16.5 pounds, while the 3rd percentile is roughly 13 pounds and the 97th percentile is about 20 pounds. For girls, the 50th percentile is around 15 pounds, with a healthy range stretching from about 12 pounds at the 3rd percentile to roughly 18.5 pounds at the 97th.
A baby at the 10th percentile is not less healthy than one at the 90th. Percentiles simply rank where your baby falls compared to other children of the same age and sex. A baby who has tracked along the 15th percentile since birth is growing exactly as expected. What raises concern is a sudden drop across percentile lines, like falling from the 50th to the 10th over a couple of months.
Birth Weight as a Baseline
One of the simplest benchmarks: healthy, full-term babies typically double their birth weight by about 4 months. So by 5 months, most babies have already passed that milestone and are continuing to gain steadily. A baby born at 7.5 pounds, for example, would generally weigh at least 15 pounds by now.
Between 3 and 6 months, a healthy rate of weight gain is at least 0.67 ounces per day, or roughly 4 to 5 ounces per week. If your baby is consistently gaining less than that, it may signal a feeding issue worth discussing with your pediatrician.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies don’t grow at the same pace, and that’s normal. Breastfed infants typically put on weight more slowly than formula-fed infants during the first year. The difference becomes especially noticeable after about 3 months, when formula-fed babies tend to gain weight more quickly. This pattern continues even after solid foods are introduced.
If your breastfed baby seems smaller than a formula-fed baby the same age, that alone isn’t a concern. The WHO growth charts your pediatrician uses are based primarily on breastfed infants, so they already account for this slower trajectory. What matters is that your baby is staying on their own curve, not matching someone else’s.
How Much a 5-Month-Old Needs to Eat
At 5 months, most babies are still exclusively on breast milk or formula. According to Johns Hopkins Medicine, formula-fed babies at this age typically drink 6 to 7 ounces per feeding, five to six times a day. That works out to roughly 30 to 42 ounces of formula in 24 hours.
Breastfed babies are harder to measure in ounces since you can’t see how much they’re taking in. Signs your baby is getting enough include consistent weight gain, six or more wet diapers a day, and a generally alert, active temperament between feedings. Most 5-month-olds haven’t started solid foods yet, though some pediatricians give the green light to begin around this time.
Weight and Length Together
Your pediatrician doesn’t look at weight in isolation. They also plot your baby’s length and head circumference, then compare weight relative to length. This weight-for-length ratio helps distinguish between a baby who is heavy because they’re long and a baby whose weight is disproportionate to their frame. The CDC flags a weight-for-length below the 2nd percentile as unusually low and above the 98th percentile as unusually high. Most babies fall comfortably between those extremes.
Premature Babies and Adjusted Age
If your baby was born early, their weight at 5 months of chronological age won’t match the charts in a straightforward way. Pediatricians use “corrected age,” which subtracts the weeks of prematurity from your baby’s actual age. A baby born 6 weeks early and now 5 months old would be plotted on the growth chart as a 3.5-month-old. This adjustment is standard practice until age 2, at which point most preemies have caught up to their full-term peers.
Signs of Slow Weight Gain
A baby who is noticeably smaller than peers the same age isn’t automatically a concern, but certain patterns deserve attention. Boston Children’s Hospital identifies several signs that a baby may not be getting enough calories: extreme sleepiness, lost interest in their surroundings, frequent crying and fussiness, and missed physical milestones like not rolling over when other babies their age are starting to. For babies between 3 and 6 months, gaining less than 0.67 ounces per day is a specific threshold that warrants a closer look.
Slow weight gain can stem from many causes, some as simple as a latch issue during breastfeeding or a formula that isn’t agreeing with your baby. It can also reflect food sensitivities, reflux, or less commonly, an underlying medical condition. In most cases, the fix is straightforward once the cause is identified. Your pediatrician tracks weight at every well-child visit precisely to catch these dips early, so keeping those appointments on schedule is one of the most useful things you can do.