A typical six-month-old weighs around 16 to 17 pounds (7.3 to 7.7 kg), though healthy babies at this age can range from roughly 13 to 21 pounds depending on sex, genetics, and feeding method. What matters more than hitting a single number is that your baby is following a consistent growth curve over time.
Average Weight at Six Months
On the World Health Organization growth charts, which are recommended in the United States for all children from birth to age 2, the 50th percentile weight for a six-month-old girl is about 16.1 pounds (7.3 kg). For boys, it’s about 17.4 pounds (7.9 kg). The 50th percentile simply means half of healthy babies weigh more and half weigh less, so falling above or below that line is completely normal.
A more practical benchmark: most healthy, full-term babies double their birth weight by about 4 months of age and triple it by their first birthday. If your baby was born at 7.5 pounds, you’d generally expect them to be well past 15 pounds by the six-month mark. Between 4 and 6 months, babies typically gain about 1 to 1.25 pounds per month, according to Children’s Hospital of Philadelphia. Growth tends to slow slightly compared to those rapid early months.
Why Percentiles Matter More Than Pounds
Pediatricians don’t focus on one weight reading in isolation. They track your baby’s percentile over multiple visits to see whether the growth curve stays relatively steady. A baby consistently tracking along the 20th percentile is growing just as normally as one at the 80th percentile. They’re simply different sizes, which is expected given the wide range of genetics at play.
The concern arises when a baby’s weight drops across two or more major percentile lines over time. For example, a baby who was at the 60th percentile at 2 months and falls to the 15th percentile by 6 months may need evaluation. This kind of pattern, sometimes called growth faltering, can signal feeding difficulties, food sensitivities, or other underlying issues. A single low reading at one visit doesn’t automatically indicate a problem.
Breastfed vs. Formula-Fed Babies
Feeding method affects weight gain patterns in the first year. Healthy breastfed infants typically put on weight more slowly than formula-fed infants, especially after about 3 months of age. Formula-fed babies tend to gain weight faster from that point forward, and these differences in weight patterns persist even after solid foods are introduced around 6 months.
This doesn’t mean breastfed babies are underfed. The WHO growth charts were specifically developed using data from breastfed infants as the standard for normal growth, which is one reason they’re preferred over older charts for children under 2. If your breastfed baby is lighter than a friend’s formula-fed baby of the same age, that’s expected and not a reason for concern on its own.
Signs of Slow Weight Gain to Watch For
Weight alone doesn’t tell the whole story. Cleveland Clinic identifies several signs that may point to growth faltering in infants:
- Not gaining weight as expected over multiple checkups
- Excessive sleepiness, including falling asleep during feedings
- Crying more than seems typical
- Reduced interaction, such as not mimicking facial expressions or engaging socially at the level expected for their age
- Not growing in length alongside weight
Any one of these in isolation may be nothing, but a combination, especially paired with a dropping growth curve, is worth raising with your pediatrician. If you’re having difficulty waking your baby for feedings, that warrants a prompt call.
Premature Babies Follow a Different Timeline
If your baby was born early, the six-month weight expectations above won’t apply directly. Growth for premature infants is tracked using corrected age, not the calendar birthday. Corrected age adjusts for how early the baby arrived. A baby born 8 weeks premature who is now 6 months old would be evaluated as a 4-month-old on growth charts.
The Agency for Healthcare Research and Quality recommends using growth charts designed specifically for premature infants during the early months, then switching to standard charts once the baby reaches the equivalent of full-term gestational age. Corrected age continues to be used for growth plotting until age 2. So if your preemie seems small for a six-month-old, the adjusted timeline may put them right on track.
How to Weigh Your Baby at Home
Your pediatrician weighs your baby at every well-child visit, but if you want to track weight between appointments, there are a few ways to get a reasonable reading at home. The most accurate approach uses a dedicated baby scale, but standard bathroom scales work too.
The simplest method: weigh yourself alone, then weigh yourself holding your undressed baby, and subtract the difference. For a slightly more precise option, place a baby bath on your bathroom scale, reset the scale to zero, then lay your naked baby in the bath and read the weight. Make sure the bath doesn’t hang over the edges of the scale or touch the floor, which would throw off the number.
For the most consistent results, weigh your baby naked, before a feeding, and around the same time of day each time. Place your scale on a hard, flat surface rather than carpet. If your baby is squirming, wait for the reading to stabilize before recording it. Don’t weigh daily, as normal fluctuations from feeding, diaper changes, and hydration will create anxiety over meaningless variation. Once a week or every two weeks gives you a much clearer picture of the actual trend.
What Influences Your Baby’s Weight
Genetics is the single biggest factor. Taller, larger parents tend to have bigger babies, and the reverse is true for smaller parents. Your baby’s birth weight sets the starting point, and most babies find their genetically programmed growth curve within the first few months of life. It’s common for a baby born large to slow down and settle into a lower percentile, or for a smaller newborn to gain rapidly and move up. This early adjustment is normal and different from the concerning percentile drops that happen later.
Sex plays a role too. Boys are typically about a pound heavier than girls at six months. Overall health, sleep quality, how efficiently a baby feeds, and whether they’ve had any illnesses can all cause temporary fluctuations. A baby recovering from a stomach bug might dip briefly before catching back up. The pattern over weeks and months is what counts, not any single weigh-in.