Newborns grow remarkably fast, gaining about 1 ounce (28 grams) per day during their first few months of life. Most babies double their birth weight by around 5 months and triple it by their first birthday. But growth isn’t a smooth, steady climb. It happens in bursts, slows down at predictable points, and varies depending on how your baby is fed and how much sleep they’re getting.
The First Week: Expect Weight Loss
Before your newborn starts gaining, they’ll actually lose weight. Nearly all babies drop some of their birth weight in the first few days, typically hitting their lowest point between days 2 and 3. For exclusively breastfed infants, this initial loss ranges from about 5.5% to 8.6% of birth weight. A baby born at 7 pounds 8 ounces, for example, might dip to around 7 pounds before the upward trend begins.
Most babies return to their birth weight by 3 weeks of age. Formula-fed infants tend to bounce back a bit faster, around 16 to 17 days, while exclusively breastfed babies may take up to 21 days. This early weight loss is normal and reflects fluid shifts after birth, not a feeding problem, as long as the baby is regaining steadily.
Weight Gain Month by Month
Once the initial dip is over, newborns pack on weight quickly. During the first three months, babies gain about 1 ounce per day, which works out to roughly half a pound per week or about 2 pounds per month. Around the 4-month mark, that pace slows to approximately 20 grams (about two-thirds of an ounce) per day.
This deceleration is completely normal. If your baby kept gaining at the newborn rate for an entire year, they’d weigh over 20 pounds by 6 months. The body naturally throttles back as the most intense period of organ development and fat accumulation levels off. What matters more than hitting a specific number is that your baby follows a consistent upward curve over time.
Breastfed vs. Formula-Fed Growth Patterns
Breastfed and formula-fed babies grow at noticeably different rates, and knowing this can save you unnecessary worry. Breastfed infants typically gain weight more slowly than formula-fed infants during the first year. Formula-fed babies tend to gain weight more quickly after about 3 months of age, and this difference persists even after solid foods are introduced.
Length growth, on the other hand, is similar regardless of feeding method. The difference is almost entirely in weight. This is one reason the CDC recommends using the World Health Organization growth charts for all children under 24 months. The older CDC charts were based primarily on formula-fed infants, which can make a perfectly healthy breastfed baby look like they’re falling behind when they’re actually growing exactly as expected. The WHO charts reflect growth patterns of babies who were predominantly breastfed for at least 4 months, making them a better standard for all infants.
Head Circumference Growth
Your baby’s head grows faster in the first few months than at any other time. From birth to 3 months, head circumference increases by about 2 centimeters per month. Between 3 and 6 months, that slows to roughly 1 centimeter per month. During the second half of the first year, it drops further to about half a centimeter per month. Pediatricians track head growth closely because it reflects brain development. A head that’s growing too fast or too slowly can signal issues that need attention, even when weight and length look fine.
When Growth Spurts Happen
Growth doesn’t follow a straight line. Babies go through predictable periods of rapid growth, typically around 2 to 3 weeks, 6 weeks, 3 months, 6 months, and 9 months. During these spurts, your baby may seem hungrier than usual, want to feed more frequently, sleep more (or less), and act fussier than normal.
Research has shown that growth in length is directly linked to sleep. Babies tend to grow longer following periods of increased napping and longer total sleep. The connection is hormonal: the body releases growth hormone in bursts shortly after falling into deep sleep. More time in deep sleep means more growth hormone, which translates to measurable increases in length. One study tracking infant growth found that episodic length increases were temporally coupled to changes in sleep, providing the first direct evidence for what parents have long suspected: babies really do seem to grow overnight.
These spurts usually last a few days to a week. If your baby suddenly wants to eat constantly, it’s likely their body gearing up for a jump in size rather than a sign that your milk supply is dropping or that they aren’t getting enough.
Signs That Growth Has Stalled
The rate of change in weight and height is often more important than any single measurement. A baby who has always tracked along the 15th percentile is doing fine. A baby who drops from the 50th percentile to the 15th over a couple of months is a different story. Pediatricians call this “failure to thrive” when a child’s weight or rate of weight gain falls significantly below other children of the same age and sex.
Specific warning signs include weight falling below the 3rd percentile on standard growth charts, weight dropping more than 20% below the ideal for the baby’s length, or a previously established growth curve that flattens or declines. Babies who aren’t growing adequately may also show delays in physical milestones like rolling over, sitting, and standing. These delays tend to follow prolonged periods of poor weight gain rather than appearing suddenly.
Slow growth can stem from feeding difficulties, underlying medical conditions, or simply not taking in enough calories. In most cases, it’s identifiable early through routine checkups, which is why those frequent well-baby visits in the first year exist. The growth chart your pediatrician fills in at each appointment isn’t just paperwork. It’s the single most reliable tool for catching problems before they become serious.