A 5-month-old boy typically weighs around 16.5 pounds (7.5 kg), while a 5-month-old girl typically weighs around 15 pounds (6.8 kg), based on the 50th percentile of the WHO growth standards. But “supposed to” covers a wide range. Babies anywhere between the 5th and 95th percentiles are generally growing normally, which means a healthy 5-month-old could weigh anywhere from about 13 to 20 pounds depending on sex, genetics, and feeding patterns.
Average Weight at 5 Months
The 50th percentile is the midpoint, meaning half of babies weigh more and half weigh less. Here’s what the WHO growth charts show for 5-month-olds:
- Boys: About 16.5 lbs (7.5 kg) at the 50th percentile, with a normal range from roughly 13.5 lbs (5th percentile) to 19.5 lbs (95th percentile)
- Girls: About 15 lbs (6.8 kg) at the 50th percentile, with a normal range from roughly 12.5 lbs (5th percentile) to 18.5 lbs (95th percentile)
What matters more than hitting any single number is your baby’s growth trend over time. A baby who has tracked along the 20th percentile since birth is growing perfectly well, even though they weigh less than average. Pediatricians plot weight at every well-child visit specifically to watch this trajectory rather than comparing one snapshot to a chart.
The Birth Weight Rule of Thumb
Most healthy, full-term newborns double their birth weight by about 4 months. So by 5 months, your baby should comfortably be past that doubling milestone. A baby born at 7.5 pounds, for example, would typically weigh at least 15 pounds by now. If your baby was premature or had a low birth weight, the timeline shifts, and your pediatrician will likely use an adjusted age for growth tracking.
Between 4 and 6 months, infants gain an average of 1 to 1.25 pounds per month. That pace is noticeably slower than the first few months of life, when weight gain is more rapid. It’s normal for the curve to flatten a bit around this age.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies often follow slightly different weight curves, and this is well documented. Healthy breastfed infants typically put on weight more slowly than formula-fed infants during the first year. Formula-fed babies tend to gain weight more quickly after about 3 months, and this difference persists even after solid foods are introduced.
This means a breastfed 5-month-old who weighs a bit less than a formula-fed peer of the same age isn’t necessarily falling behind. The WHO growth charts, which most pediatricians use for children under 2, were designed based on breastfed infants and account for this pattern. If your pediatrician is using older CDC charts (more common for children over 2), a breastfed baby might appear to be gaining slowly when they’re actually right on track.
How Much a 5-Month-Old Eats
At this age, breast milk or formula is still the sole or primary source of nutrition. Formula-fed babies typically take 6 to 7 ounces per feeding, five to six times a day, which works out to roughly 30 to 42 ounces in 24 hours. Breastfed babies nurse on demand, usually every 3 to 4 hours, and intake is harder to measure precisely.
Some families start introducing small amounts of pureed foods around this age, but solid food at 5 months is more about exposure and motor skill development than calories. The bulk of your baby’s nutrition and weight gain still comes from milk.
One simple way to tell if your baby is getting enough: diaper output. By this age, babies should be producing at least 6 to 10 wet diapers per day. Consistently fewer wet diapers can signal inadequate intake and is worth bringing up with your pediatrician.
When Weight Trends Are Concerning
A single weigh-in that falls on a lower percentile isn’t automatically a problem. Babies shift around on the growth chart, and crossing a percentile line can be completely normal. What pediatricians watch for is a pattern: consistent downward movement across two or more major percentile lines over several visits.
The specific pattern of the drop matters too. When a baby’s weight falls first and their length drops a few months later, the likely explanation is not getting enough calories. This is different from a situation where weight and length fall off at the same time while staying proportional to each other, which can point to a hormonal or endocrine issue rather than a feeding problem.
Babies who were small for gestational age at birth are expected to show catch-up growth in the early months. If that catch-up isn’t happening despite adequate feeding, it typically leads to a referral for more specialized nutritional support.
Factors That Affect Your Baby’s Weight
Genetics play a large role. Tall, lean parents tend to have longer, leaner babies. Shorter, stockier parents often have babies who are heavier for their length. Your baby’s birth weight, whether they were premature, and their sex all influence where they land on the chart at 5 months.
Illness can cause temporary dips. A stomach bug or a few days of poor feeding from a cold can slow weight gain for a week or two, but most babies bounce back quickly. Growth spurts also create uneven patterns, where a baby might gain very little for two weeks and then put on a full pound in the next two.
The most useful thing you can do is keep your well-child appointments so your pediatrician can plot multiple data points over time. A single number on the scale tells you very little. The shape of the curve tells you almost everything.