Most 6-month-old babies weigh between 14 and 18 pounds, though the healthy range is wider than many parents expect. A boy at the 50th percentile weighs about 17.5 pounds at 6 months, while a girl at the 50th percentile weighs about 16 pounds. But percentiles are a range, not a target, and a baby tracking steadily along the 15th percentile is just as healthy as one cruising along the 75th.
Average Weight at 6 Months
The World Health Organization growth standards, which the CDC recommends for all U.S. children from birth to age 2, put the 50th percentile weight for 6-month-old boys at roughly 17.5 pounds (7.9 kg) and for girls at roughly 16.1 pounds (7.3 kg). The full normal range stretches from around 13 pounds at the lower percentiles to over 20 pounds at the higher ones.
What matters more than hitting a specific number is where your baby falls on the growth curve relative to where they started. A baby born in the 25th percentile who stays near the 25th percentile is growing exactly as expected. Pediatricians track the trajectory over multiple visits rather than judging any single weigh-in.
The “Double Your Birth Weight” Rule
You’ve probably heard that babies should double their birth weight by 5 or 6 months. That guideline is roughly right, but the real average is a bit earlier. A study of 357 healthy infants found the mean age for doubling birth weight was 119 days, or about 3.8 months. Boys hit that milestone slightly sooner (around 111 days) than girls (around 129 days), and formula-fed babies doubled a bit earlier than breastfed babies (113 days versus 124 days).
So by 6 months, most babies have already passed the doubling mark. If your baby was born at 7 pounds, you’d expect them to be well above 14 pounds by now. If your baby was born smaller or larger than average, adjust your expectations accordingly. A baby born at 5.5 pounds will look very different from one born at 9 pounds, and both can be perfectly on track.
How Feeding Method Affects Weight
Breastfed and formula-fed babies grow differently, and it’s important to know this so you don’t worry unnecessarily. Healthy breastfed infants typically put on weight more slowly than formula-fed infants during the first year. Formula-fed babies tend to gain weight faster after about 3 months of age, and that difference persists even after solid foods enter the picture. Length growth, on the other hand, is similar regardless of feeding method.
This is one reason the CDC recommends the WHO growth charts for children under 2. The WHO charts are based on breastfed infants as the standard, so a breastfed baby who looks like they’re “falling behind” on older charts may actually be growing normally. If your pediatrician is using the WHO charts (most do now), the percentiles already account for these differences.
What About Starting Solids?
Six months is when most families begin introducing solid foods, and it’s natural to wonder whether this will change your baby’s weight gain. Research suggests it doesn’t, at least not right away. A study tracking infants through their first year found no association between the timing of solid food introduction and weight gain. Babies appear to self-regulate their total calorie intake: as they eat more solid food, they take in slightly less breast milk or formula, keeping their overall energy intake steady. So don’t expect a sudden jump on the scale just because your baby starts eating rice cereal or pureed sweet potatoes.
Typical Weight Gain at This Age
Between 4 and 6 months, babies gain about 1 to 1.25 pounds per month on average. That’s noticeably slower than the rapid gains of the first few months, when some newborns pack on close to 2 pounds monthly. This slowdown is normal. Growth rate continues to taper through the second half of the first year, especially once babies become more mobile and burn more energy crawling and pulling up.
When Weight Is a Concern
Pediatricians look at patterns, not single data points. The red flags they watch for are specific: a weight-for-age below the 5th percentile, a drop crossing two or more major percentile lines on the growth chart, or actual weight loss between visits. A baby who has always tracked along a lower percentile is far less concerning than one who was at the 60th percentile at 2 months and has fallen to the 15th by 6 months.
Context matters too. Premature babies are plotted on growth charts using their corrected age (counting from their due date, not their birth date), so a preemie born two months early would be compared against 4-month norms at their 6-month birthday. Genetics also play a significant role. Smaller parents tend to have smaller babies, and a baby settling into a lower percentile after the first few months can simply be finding their genetic growth channel.
If your baby is gaining weight steadily, producing plenty of wet diapers, meeting developmental milestones, and seems alert and content, they’re almost certainly fine, even if they’re lighter or heavier than the average. The number on the scale is just one piece of a much bigger picture.