A 5-month-old baby typically weighs around 14 to 17 pounds if male, or 13 to 16 pounds if female, based on the 25th to 75th percentile range on standard growth charts. But the number on the scale matters far less than whether your baby is growing consistently along their own curve. A baby tracking steadily at the 15th percentile is just as healthy as one at the 85th.
Average Weight at 5 Months
The 50th percentile, the statistical middle, for a 5-month-old boy is roughly 16 pounds (7.5 kg). For a 5-month-old girl, it’s about 14.5 pounds (6.7 kg). These numbers come from the WHO growth standards, which are based on healthy breastfed infants from multiple countries. Your pediatrician plots your baby’s weight on these charts at each well-child visit.
A useful rule of thumb: most babies double their birth weight by about 4 months of age. Research on 357 healthy infants found the average doubling time was 119 days, or just under 4 months. Boys tended to hit this milestone a bit earlier (around 111 days) than girls (around 129 days). So by 5 months, your baby has likely already passed the double-birth-weight mark, and some are well beyond it.
Why the Growth Curve Matters More Than One Number
Pediatricians care less about any single weight reading and more about the pattern over time. A baby who has been tracking along the 20th percentile since birth is following a perfectly normal trajectory. What raises concern is crossing percentile lines, either up or down. Dropping across two or more major percentile lines (for example, falling from the 50th to the 10th) is a traditional signal of faltering growth. In the same way, a rapid upward jump across several lines can flag overfeeding.
This is why comparing your baby’s weight to a friend’s baby is not very useful. Genetics, birth size, feeding method, and overall health all influence where a baby sits on the chart. The important question is: is your baby following a consistent path?
How Fast Should a 5-Month-Old Gain Weight?
Weight gain naturally slows as babies get older. In the first few months, babies gain about 1 ounce (28 grams) per day. By 4 months, that drops to around 20 grams per day. And by 6 months, many babies are gaining 10 grams or less per day. So at 5 months, your baby is right in the middle of that slowdown, likely gaining somewhere around half an ounce per day, or roughly 3 to 4 pounds over the course of that month.
This deceleration is completely normal and catches some parents off guard. If your baby seemed to be packing on weight quickly in the early months and now appears to be slowing, that’s expected biology, not a problem.
Breastfed vs. Formula-Fed Weight Differences
How you feed your baby affects their growth pattern. Breastfed babies typically gain weight more slowly than formula-fed babies after about 3 months of age, and this difference persists even after solid foods are introduced. The CDC notes that length (height) growth is similar between the two groups, so the difference is specifically in weight.
Research on birth weight doubling found that formula-fed infants doubled their weight earlier (around 113 days) compared to breastfed infants (around 124 days). The formula-fed group also tended to be heavier relative to their length, sitting around the 75th percentile for weight but only the 55th for length. Breastfed infants showed a more proportional pattern, with weight and length both near the 55th to 60th percentiles.
This means a breastfed 5-month-old who weighs a pound or two less than a formula-fed peer is not falling behind. The WHO growth charts your pediatrician uses were specifically designed around breastfed infants to reflect this normal variation.
Premature Babies Need Adjusted Age
If your baby was born prematurely, their weight should be compared against their corrected age, not their actual birth date. Corrected age subtracts the weeks of prematurity. A baby born 6 weeks early who is now 5 months old by the calendar would be assessed as a 3.5-month-old for growth purposes.
This adjustment is recommended until age 2. Premature infants may also need specialized growth charts in their early months, particularly if they spent time in the NICU. Once they reach their original due date equivalent, standard growth charts apply, but always using the corrected age.
Feeding Needs That Support Healthy Growth
At 5 months, breast milk or formula remains your baby’s sole nutrition source (most guidelines recommend waiting until around 6 months to introduce solids). A healthy infant needs roughly 100 calories per kilogram of body weight per day. For a 15-pound baby (about 6.8 kg), that works out to around 680 calories daily, which translates to approximately 24 to 32 ounces of breast milk or formula spread across the day.
Babies are generally good at regulating their own intake. If your baby is eating well, producing plenty of wet diapers, and staying on their growth curve, their calorie intake is likely right where it needs to be.
Signs That Weight May Be a Concern
A single low or high weight reading is rarely meaningful on its own. Pediatricians look for patterns and context. Growth that falls below the 5th percentile for age, or a drop of more than two major percentile lines on the chart, can indicate faltering growth. Actual weight loss between visits, rather than just slower gain, is a red flag at any percentile.
Physical signs that sometimes accompany poor weight gain include fatigue or heavy sweating during feeding, blood or mucus in the stool, large foul-smelling stools, and low muscle tone. On their own, none of these are diagnostic, but paired with a concerning growth pattern, they help your pediatrician determine whether further evaluation is needed.
On the other end, rapid weight gain that outpaces length growth can signal overfeeding, particularly in formula-fed babies. If your baby’s weight percentile is climbing steeply while their length stays flat, it’s worth discussing feeding volumes and frequency with your pediatrician.