A 6-month-old baby typically weighs between 14 and 21 pounds, with the average falling around 17 to 18 pounds. The exact number depends on sex, birth weight, and whether your baby is breastfed or formula-fed. Here’s what the ranges look like and what actually matters when it comes to your baby’s growth.
Average Weight for 6-Month-Old Boys and Girls
The World Health Organization growth charts, used by pediatricians in the U.S. and internationally, put the 50th percentile weight for a 6-month-old boy at 7.9 kg, or about 17.4 pounds. Girls at the same age tend to be slightly lighter, with an average closer to 16.1 pounds.
The healthy range is wide. A boy at the 5th percentile weighs around 14.1 pounds, while one at the 95th percentile weighs about 21.4 pounds. Both are considered normal. “Percentile” just means where your baby falls compared to other babies the same age. A baby at the 25th percentile isn’t underweight; it means 25% of babies weigh less and 75% weigh more.
The number that matters most isn’t where your baby lands on the chart at any single visit. It’s the pattern over time. A baby who’s been tracking along the 20th percentile since birth is growing normally. A baby who was at the 60th percentile and has dropped to the 15th over two or three visits may need a closer look.
How Fast Babies Gain Weight at This Age
Weight gain slows down considerably by six months, and that catches some parents off guard. In the first few months of life, babies gain roughly an ounce a day. By four months, that drops to about 20 grams (just under three-quarters of an ounce) per day. Around six months, many babies are gaining 10 grams or less daily, which works out to roughly a pound or less per month.
A common rule of thumb: most healthy, full-term babies double their birth weight by four months and triple it by their first birthday. So if your baby was born at 7.5 pounds, you’d expect something in the neighborhood of 15 pounds by four months and 22 to 23 pounds by 12 months. These are rough guidelines, not exact targets. Premature babies and babies born particularly large or small will follow different trajectories.
Breastfed vs. Formula-Fed Growth Patterns
If your baby is breastfed and seems lighter than formula-fed babies the same age, that’s expected. Breastfed infants typically gain weight more slowly than formula-fed infants, especially after about three months. The difference continues even after starting solid foods around six months.
This doesn’t mean breastfed babies are less healthy or less nourished. Their length growth is similar to formula-fed babies. The WHO growth charts were actually built using breastfed infants as the standard, which is one reason the CDC recommends using the WHO charts for all children under two regardless of feeding method. If your pediatrician is using these charts, the percentiles already account for typical breastfed growth.
What Starting Solids Means for Weight
Six months is when most babies start solid foods, which can subtly shift weight gain patterns. Early on, solids are more about learning to eat than about calories. Your baby might take a few spoonfuls of pureed vegetables or iron-fortified cereal, but breast milk or formula still provides the bulk of their nutrition.
Some parents notice a small uptick in weight gain once solids are established, while others see no obvious change. Both are normal. The transition to solids is gradual, and it typically takes weeks before your baby is eating enough food to meaningfully affect the number on the scale.
When Weight Actually Signals a Problem
Pediatricians look for specific patterns rather than single data points. A weight below the 5th percentile, or a drop that crosses two or more percentile lines on the growth chart, can indicate growth faltering (what used to be called “failure to thrive”). Doctors use a statistical measurement called a z-score to quantify how far a baby’s weight falls from the average and to track whether the trend is worsening.
Not every percentile drop is concerning. Babies born large for their gestational age often settle into a lower percentile in the first few months, and that’s a normal correction, not a red flag. What clinicians are watching for is a sustained downward trend without an obvious explanation.
Signs that often accompany genuine growth concerns include fewer than four wet diapers a day, lethargy or unusual irritability, and consistently poor feeding. A baby who is alert, meeting developmental milestones, and producing plenty of wet diapers is unlikely to have a serious growth issue even if their weight percentile seems low.
Making Sense of Your Baby’s Number
It’s tempting to compare your baby’s weight to a friend’s baby or to an online average, but individual variation is enormous. Genetics play a major role. Two healthy parents who are on the shorter, lighter side will likely have a baby who tracks along lower percentiles, and that’s exactly where that baby should be.
What you want to see is consistency. A baby following their own curve, whatever that curve is, is a baby who’s growing well. If you’re tracking your baby’s weight at home between pediatric visits, weigh them at roughly the same time of day, in the same clothing (or no clothing), on the same scale. Small differences in these variables can swing the reading by several ounces, which is a meaningful amount when you’re only expecting a few ounces of gain per week at this age.