Most 4-month-old boys weigh between 13 and 18 pounds, while most girls weigh between 12 and 17 pounds. The average sits around 15 pounds for boys and 14 pounds for girls. But healthy babies come in a wide range of sizes, and your baby’s individual growth pattern matters more than hitting one specific number.
What the Growth Charts Actually Show
Pediatricians in the United States use the World Health Organization (WHO) growth standards for all children from birth to age 2, whether breastfed or formula-fed. Both the CDC and the American Academy of Pediatrics recommend these charts. They don’t show a single “correct” weight. Instead, they show percentiles, which tell you how your baby compares to a large population of healthy infants.
A baby in the 25th percentile isn’t too small, and a baby in the 85th percentile isn’t too big. Both are normal. What your pediatrician watches most closely is whether your baby stays on a consistent curve over time. A baby who has tracked along the 30th percentile since birth and continues doing so at 4 months is growing exactly as expected. A baby who drops from the 70th percentile to the 20th in a short period would warrant a closer look, even though 20th percentile is perfectly healthy on its own.
How Fast Babies Gain Weight at This Age
Between 4 and 6 months, babies typically gain about 1 to 1.25 pounds per month. That works out to roughly 4 to 5 ounces per week. This is actually a bit slower than the newborn pace. In the first few months of life, babies gain about 1 ounce per day. Around 4 months, that rate drops to about 20 grams (just under three-quarters of an ounce) per day.
This slowdown is completely normal and doesn’t mean your baby isn’t eating enough. It’s simply the natural shift as your baby’s growth rate stabilizes. Many babies roughly double their birth weight by around 4 to 5 months, so if your baby was born at 7.5 pounds, a weight of 14 to 15 pounds at the 4-month checkup is right on track.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies often weigh about the same at 4 months, but their growth patterns start diverging around this age. Formula-fed babies typically gain weight more quickly after about 3 months, while breastfed babies put on weight more slowly through the rest of the first year. These differences persist even after babies start solid foods.
Importantly, both groups grow in length at similar rates. The weight difference isn’t a sign that breastfed babies are underfed. It reflects the different composition of breast milk and formula and how babies’ bodies process each one. The WHO growth charts were built primarily from data on breastfed infants, which is one reason the CDC recommends them for all babies under 2.
What Influences Your Baby’s Weight
Genetics play the biggest role. Tall, large-framed parents tend to have bigger babies, and smaller parents tend to have smaller ones. Birth weight also sets the starting point: a baby born at 6 pounds will likely weigh less at 4 months than one born at 9 pounds, even if both are growing at perfectly healthy rates.
Sex matters too. Boys at 4 months are typically about a pound heavier than girls on average. And while feeding type (breast milk or formula) creates some differences in growth speed, both approaches support healthy development when babies are eating enough.
A 4-month-old needs roughly 82 calories per kilogram of body weight each day. For a 14-pound baby, that’s about 520 calories daily. You don’t need to count your baby’s calories, but this is why pediatricians ask about feeding frequency. At this age, most babies eat 4 to 6 times per day if breastfed, or take 4 to 5 bottles of 6 to 8 ounces if formula-fed.
Signs Your Baby Is Getting Enough
Rather than weighing your baby at home between checkups, the easier way to gauge adequate intake is output. A 4-month-old who is eating well produces several wet diapers per day and has regular bowel movements. The baby should seem satisfied after feedings, be alert and active during wake times, and have good skin color and muscle tone.
Steady weight gain at regular checkups confirms the picture. Your pediatrician weighs your baby at every well-child visit, and the 4-month visit is specifically designed to catch any growth concerns early.
Adjusted Age for Premature Babies
If your baby was born early, the numbers above won’t apply the same way. Premature infants are tracked using corrected age, which is calculated from their original due date rather than their actual birth date. A baby born 6 weeks early who is now 4 months old would be evaluated as a 2.5-month-old on the growth chart.
Pediatricians use corrected age for growth assessments until age 2. Very premature babies may also be plotted on growth charts designed specifically for preterm infants during the earliest months. If your baby was premature, their care team will guide you on which milestones and weight ranges to expect and when.
When Weight Falls Outside the Expected Range
A single weight reading that’s high or low on the growth chart is rarely cause for concern by itself. Pediatricians look at the trend across multiple visits. A baby who has always been small but is growing steadily is healthy. A baby whose weight gain has stalled or whose curve is crossing percentile lines downward may need a feeding evaluation.
On the other end, rapid upward percentile crossing can sometimes signal overfeeding, particularly in formula-fed infants. But again, one data point doesn’t tell the story. The pattern over time, combined with your baby’s length and head circumference, gives a much fuller picture of whether growth is on track.