Babies grow remarkably fast in their first year, gaining about 10 inches in length and typically tripling their birth weight by around 12 months. That pace of growth is faster than any other period of life outside the womb, and it follows a predictable pattern that slows gradually as the year progresses.
The First Two Weeks
Almost every newborn loses weight in the first few days after birth. This is normal and expected. Most of it is fluid loss as the baby adjusts to life outside the womb. A healthy newborn should regain their birth weight within 10 to 14 days. If that doesn’t happen, it can signal a feeding issue worth addressing early.
Weight Gain From Birth to 6 Months
Once babies start gaining, the early months are the fastest. In the first few months, most infants put on about 1 ounce (28 grams) per day. That works out to roughly half a pound per week, or about two pounds per month. You can almost watch it happen in real time: clothes that fit one week feel snug the next.
Around 4 months, the rate starts to slow to about 20 grams per day. By 6 months, many babies are gaining 10 grams or less per day. This gradual slowdown is completely normal. Most healthy, full-term babies double their birth weight by 4 months, so a baby born at 7.5 pounds will typically weigh around 15 pounds by that point.
Weight Gain From 6 to 12 Months
The second half of the first year is noticeably slower. Babies are still growing, but the dramatic weight jumps of those early months taper off. That daily gain of 10 grams or less continues through this period, meaning monthly weight gain might be a pound or even less. By 12 months, most babies have tripled their birth weight. A baby born at 7.5 pounds would weigh somewhere around 22 to 23 pounds at their first birthday.
Parents sometimes worry during this phase because the numbers on the scale don’t climb as quickly. But this is also when babies become far more active, rolling, crawling, and eventually pulling to stand, which burns more energy and naturally slows weight gain relative to those sleepy early months.
How Quickly Babies Get Longer
Length follows a steadier trajectory than weight. On average, babies grow just over half an inch per month, adding up to about 10 inches over the first year. A baby born at 20 inches will typically measure around 30 inches by their first birthday.
Unlike weight, length growth is fairly consistent between breastfed and formula-fed babies. The CDC notes that linear growth patterns are similar regardless of feeding method, even though weight patterns differ.
Breastfed vs. Formula-Fed Growth
Breastfed and formula-fed babies don’t gain weight at the same rate, and the difference becomes noticeable after the first few months. 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 that difference persists even after solid foods are introduced.
This doesn’t mean one pattern is healthier than the other, but it does matter for how you read a growth chart. The WHO growth charts, recommended for all U.S. children from birth to age 2, are based on the growth of breastfed infants in optimal conditions. If your pediatrician is using these charts, a breastfed baby tracking along the 40th percentile is growing exactly as expected, not falling behind.
When Growth Spurts Happen
Growth doesn’t happen at a perfectly even pace. Babies go through spurts, short periods of accelerated growth that often come with increased fussiness, extra hunger, and more frequent feeding (sometimes called cluster feeding). The most common times for growth spurts are around 2 to 3 weeks, 6 weeks, 3 months, and 6 months.
During a spurt, your baby may want to eat significantly more often for a few days. A breastfed baby who had settled into a predictable feeding schedule might suddenly want to nurse every hour. This usually resolves within two to three days as the baby’s appetite returns to normal. Every baby is different, though, and spurts can happen at times that don’t match the typical schedule at all.
Growth in Premature Babies
Babies born early follow a different timeline. Premature infants are typically smaller at birth and may grow more slowly in the initial weeks, but most eventually catch up to the size of their full-term peers. This catch-up growth usually closes the gap by 12 to 18 months of age, though for some preemies, particularly those born very early, it can continue gradually for up to 5 to 7 years.
Pediatricians track premature babies using a “corrected age,” which adjusts for how early they were born. A baby born two months early will be compared on growth charts to babies two months younger, not to their actual birth date peers. This corrected age gives a much more accurate picture of whether growth is on track.
What Growth Charts Actually Tell You
Growth charts plot your baby’s weight, length, and head circumference against thousands of other children the same age. The result is a percentile, a number that shows where your baby falls relative to others. A baby at the 25th percentile for weight isn’t underweight. It means 25% of babies weigh less and 75% weigh more. What matters most isn’t the specific percentile but whether your baby follows a consistent curve over time.
A baby who has been tracking along the 30th percentile for months and suddenly drops to the 5th percentile deserves a closer look. A baby who has always been at the 10th percentile and stays there is growing exactly as their body intends. Pediatricians look for sustained patterns, not single data points, when evaluating whether growth is a concern.