During the first few months of life, babies gain about 1 ounce (28 grams) per day. That pace slows steadily over the first year, dropping to roughly 20 grams a day by 4 months and 10 grams or less by 6 months. These are averages, and healthy babies can fall above or below them, but they give you a reliable baseline for what to expect at each stage.
Weight Gain by Age
The fastest growth happens right away. In the first three months, that 1-ounce-per-day rate translates to roughly 5 to 7 ounces per week, or about 1.5 to 2 pounds per month. Most babies double their birth weight by around 4 to 5 months.
Between 4 and 6 months, the pace eases noticeably. At 20 grams per day, your baby is putting on closer to 1 pound per month. By 6 months, daily gains drop to about 10 grams, which works out to roughly half a pound per month or a little more. By 12 months, most babies have tripled their birth weight. A baby born at 7.5 pounds, for example, typically weighs somewhere around 22 to 23 pounds at their first birthday.
It helps to think of this as a curve that flattens over time, not a straight line. A baby who was gaining an ounce a day at 2 months and slows to half that by 7 months isn’t falling behind. That deceleration is normal and expected.
Growth Spurts and Temporary Changes
Babies don’t grow at a perfectly steady rate. Growth spurts, periods of unusually rapid gain, typically happen at around 2 to 3 weeks, 6 weeks, 3 months, and 6 months. During these stretches your baby may seem hungrier than usual, want to nurse or bottle-feed more frequently, and be fussier between feedings.
A growth spurt usually lasts a few days. Breastfed babies often cluster feed during this time, nursing many times in a short window. This increased demand signals the body to produce more milk, so following your baby’s hunger cues is the most effective response. After the spurt passes, feeding patterns typically return to normal.
How Your Baby’s Growth Is Tracked
Pediatricians don’t rely on a single weigh-in. They plot your baby’s weight on a standardized growth chart at every well-child visit, looking at the overall trend over weeks and months. For babies under 2 years old, both the CDC and the American Academy of Pediatrics recommend using the World Health Organization growth charts. These charts were built from data on breastfed infants across multiple countries and are considered the best standard for all babies in this age range, regardless of whether they’re breastfed or formula-fed.
What matters most is that your baby follows a consistent curve, not that they hit a specific percentile. A baby tracking along the 25th percentile visit after visit is growing well. A baby who drops from the 60th percentile to the 15th over two or three visits may need closer attention, even though the 15th percentile itself is perfectly normal.
For babies under 6 months, your pediatrician may also look at BMI-for-age in addition to weight-for-length. Research has shown that BMI at 2 months is actually a better predictor of weight status at age 2 than weight-for-length alone, so some clinicians use it as an early screening tool for both undernutrition and overnutrition.
Signs of Slow Weight Gain
The American Academy of Pediatrics uses specific thresholds to identify babies whose weight gain may be falling short. A baby whose weight-for-length drops below the 5th percentile, whose rate of weight gain falls below the 2.3rd percentile for their age, or whose growth curve drops by a full standard deviation or more from where it was tracking may be diagnosed with “faltering weight,” the clinical term for what used to be called failure to thrive.
In practical terms, warning signs you can watch for at home include consistently fewer than six wet diapers per day after the first week, a baby who seems unsatisfied or lethargic after feeding, or visible signs like loose skin or a sunken fontanelle (the soft spot on top of the head). Some babies are simply smaller and gain slowly but steadily. The concern arises when the pattern changes, when a baby who was gaining well suddenly stalls or loses ground.
What Affects How Fast a Baby Gains
Genetics plays a significant role. Smaller parents tend to have smaller babies, and a baby’s growth often reflects their family’s build more than any feeding issue. Babies born large sometimes grow more slowly in the early months as they settle toward their genetic trajectory, and babies born small sometimes gain quickly to catch up.
Feeding method matters too, though perhaps less than many parents expect. Breastfed babies tend to gain weight rapidly in the first 3 months and then slow down compared to formula-fed babies, who often maintain a more linear pace. This is one reason the WHO charts, based on breastfed infants, are preferred for all babies under 2. Older CDC charts were built from a mix of feeding types and could make a healthy breastfed baby look like they were lagging when they weren’t.
Calorie needs are highest in the earliest months. Babies under 6 months require roughly 110 to 120 calories per kilogram of body weight each day. By age 1, that drops to 95 to 100 calories per kilogram. These numbers explain why newborns seem to eat constantly relative to their size: their metabolic demands for growth are enormous.
Weight Gain for Premature Babies
Premature babies follow a different timeline. Once a preemie weighs more than about 4.4 pounds (2 kilograms), the target is 20 to 30 grams per day. In the first month after birth, some preemies gain as much as 40 grams daily. By 4 months the expected range is 15 to 25 grams per day, and by 12 months it drops to 9 to 12 grams per day, converging with full-term averages.
Premature babies are tracked using their corrected age (age from the original due date, not the actual birth date) until at least 2 years. A baby born 8 weeks early and now 4 months old would be plotted on the growth chart as a 2-month-old. This adjustment prevents healthy preemies from being flagged as underweight when they’re simply following an appropriate, slightly delayed trajectory. Your pediatrician will let you know when it’s appropriate to stop using corrected age for growth assessment.