The average 6-month-old baby weighs about 16 to 17.5 pounds, depending on sex. Boys tend to be slightly heavier than girls at this age. But “average” is just the midpoint of a wide healthy range, and where your baby falls on that range matters less than whether they’re growing consistently over time.
Average Weight at 6 Months
For girls at 6 months, the 50th percentile (the statistical middle) is 7.3 kg, or about 16.1 pounds. The healthy range stretches from roughly 12.8 pounds at the 5th percentile to 20.5 pounds at the 95th percentile, based on the WHO growth standards the CDC recommends for all U.S. children under age 2. Boys at the same age run about a pound heavier on average, with a 50th percentile around 17.5 pounds.
A baby at the 15th percentile is just as healthy as one at the 85th percentile. Percentiles describe where a baby sits relative to other babies of the same age and sex. They aren’t grades. What pediatricians actually watch for is whether your baby stays near the same percentile over several months, not which number that percentile happens to be.
How Much Weight Babies Gain Each Month
Between 4 and 6 months, most babies gain about 1 to 1.25 pounds per month. That’s noticeably slower than the rapid weight gain of the first few months, and it continues to taper. By the time babies reach 6 months, many are gaining only about 10 grams a day (roughly 2 ounces per week), compared to about 20 grams a day at 4 months.
This slowdown is completely normal. Babies are burning more calories as they become more active, rolling, reaching, sitting up, and exploring. Parents sometimes worry when growth seems to stall, but the deceleration is expected and built into the growth charts your pediatrician uses.
The Birth Weight Doubling Rule
A commonly used milestone: most term infants double their birth weight by 4 to 5 months, according to the American Academy of Pediatrics. So by 6 months, the majority of babies have already passed that marker. If your baby was born at 7.5 pounds, you’d expect them to be somewhere around 15 pounds or more by the half-year mark. Babies born smaller or larger will hit different absolute numbers, but the doubling pattern holds across a wide range of birth weights. By their first birthday, most babies will have tripled their birth weight.
Breastfed vs. Formula-Fed Babies
Feeding method affects weight patterns more than many parents realize. Healthy breastfed infants typically put on weight more slowly than formula-fed infants during the first year, with the difference becoming more noticeable after about 3 months. Formula-fed babies tend to gain weight faster from that point on, and the gap persists even after solid foods enter the picture.
This doesn’t mean breastfed babies are underweight or underfed. The WHO growth charts, which are the recommended standard for children under 2, were built primarily from data on breastfed infants. So a breastfed baby tracking along the 30th percentile on those charts is growing exactly as expected. If your baby’s pediatrician uses older charts designed around formula-fed norms, a healthy breastfed baby can look like they’re falling behind when they’re not. It’s worth asking which chart your provider uses.
One reassuring detail: linear growth (length) is similar between breastfed and formula-fed babies. The difference is mainly in how quickly they accumulate body fat.
When Percentile Changes Matter
Babies don’t always stay locked onto a single percentile line. Small fluctuations are normal, especially around times of illness, teething, or transitions like starting solid foods. What raises concern is a sustained shift, for instance, a baby who was tracking along the 50th percentile and drops to the 15th over two or three visits, or one who jumps sharply upward in a short period.
A single weigh-in that looks off isn’t usually meaningful. Babies can weigh differently depending on when they last ate, whether their diaper is full, and even which scale is used. Pediatricians look at the trend across multiple checkups rather than any single data point. If your baby seems to be crossing percentile lines in either direction, your doctor will likely want to check in more frequently before drawing conclusions.
Signs of Healthy Growth Beyond the Scale
Weight is just one measure of how well a baby is growing. At 6 months, other signs that your baby is getting enough nutrition include consistent wet diapers (at least six per day), steady gains in length, increasing strength and motor skills like sitting with support or reaching for objects, and general alertness and energy. A baby who is active, hitting developmental milestones, and producing plenty of wet diapers is almost certainly growing well, even if their weight percentile isn’t what you expected.
Babies also start solid foods around this age, which can temporarily change weight gain patterns as they adjust to new calories and new digestive demands. Some babies take to solids quickly and gain a little faster. Others are slow to warm up and may plateau briefly. Both patterns are normal in the early weeks of complementary feeding.