Most 6-month-old babies weigh between 14 and 18 pounds, though healthy weights span a wider range depending on sex, birth weight, and feeding method. A common rule of thumb: babies typically double their birth weight by 6 months. So if your baby was born at 7.5 pounds, you’d expect them to be around 15 pounds at the half-year mark.
Average Weight by Sex
The World Health Organization growth standards, which the CDC recommends for all children under 2, show a consistent difference between boys and girls at 6 months. Boys at the 50th percentile weigh about 17.5 pounds (7.9 kg), while girls at the 50th percentile weigh about 16.1 pounds (7.3 kg). The 50th percentile means half of babies weigh more and half weigh less.
But “average” isn’t the same as “normal.” A baby at the 15th percentile is just as healthy as one at the 85th percentile, as long as they’re growing steadily along their own curve. Here’s what the range looks like:
- Boys (5th to 95th percentile): roughly 14.5 to 21 pounds
- Girls (5th to 95th percentile): roughly 13.5 to 19.5 pounds
How Growth Slows Around 6 Months
Babies gain weight fastest in the first few months of life, then gradually slow down. By 6 months, many babies gain about 10 grams or less per day, which works out to roughly 2 to 3 ounces per week. Compare that to the early months, when a healthy infant gains at least a pound per month for the first four months.
This slowdown is completely normal and catches many parents off guard. You might notice your baby’s cheeks aren’t filling out as fast, or that monthly weigh-ins show smaller jumps than before. That’s expected. Babies are becoming more active, rolling, sitting, and burning more energy, which naturally slows the pace of weight gain.
Breastfed vs. Formula-Fed Babies
How your baby eats affects their growth pattern more than most parents realize. Breastfed babies typically put on weight more slowly than formula-fed babies, especially after the 3-month mark. This difference continues even after solid foods are introduced around 6 months.
This means a breastfed baby who tracks along the 30th percentile may be growing perfectly well, even if a formula-fed baby of the same age sits at the 50th. Pediatricians expect this variation and use the WHO growth charts precisely because they’re based on breastfed infants as the standard. If your breastfed baby seems lighter than formula-fed babies you know, that alone isn’t a concern.
What Matters More Than the Number
Pediatricians care less about a single weight measurement and more about the trend over time. A baby who has tracked along the 25th percentile since birth is doing great. A baby who was at the 75th percentile at 2 months and dropped to the 25th by 6 months would raise questions, even though 25th percentile is perfectly normal on its own.
The key signal doctors watch for is a dramatic drop from a baby’s established growth curve. One slightly lower weigh-in can happen for all sorts of reasons (a recent illness, a growth spurt that hasn’t caught up yet), but a sustained downward trend across two or three visits suggests something worth investigating. On the flip side, a sudden sharp increase in weight percentile can also warrant a closer look.
Signs of Slow Weight Gain
While most babies grow just fine, there are patterns that signal a problem. For the first four months, a healthy baby should gain at least one pound per month, measured from their lowest weight after birth (babies typically lose a few ounces in the first days). After that initial period, the expected rate drops, but your baby should still be following a roughly predictable curve.
Other things pediatricians look at alongside weight include length and head circumference. If all three measurements are low but tracking steadily, your baby may simply be small. If weight is dropping while length stays on track, that’s a different picture and one that may point to a feeding or absorption issue.
Adjusting for Premature Birth
If your baby was born early, their weight at 6 months of actual age will likely be lower than the charts suggest, and that’s expected. Doctors use “corrected age” to assess preemie growth. You calculate it by subtracting the number of weeks your baby was born early from their actual age. A baby born at 32 weeks (8 weeks early) who is now 6 months old would be evaluated as a 4-month-old on growth charts.
To figure out how early your baby was, subtract their gestational age at birth from 40 weeks. Most pediatricians continue using corrected age for growth assessments until a child is about 2 years old, by which point most preemies have caught up to their peers.
The Birth Weight Doubling Rule
The simplest benchmark for 6-month weight is the doubling rule: most babies double their birth weight by around 6 months. This guideline works across a wide range of birth weights. A baby born at 6 pounds would be expected around 12 pounds; one born at 9 pounds, around 18 pounds. It’s a rough guide rather than a strict cutoff, but it gives you a quick way to check whether your baby’s growth is in the right ballpark without needing a percentile chart.
By 12 months, most babies will have tripled their birth weight, so the pace of gain in the second half of the first year stays meaningful even though it’s slower month to month than it was earlier.