A 5-month-old baby typically weighs between 12 and 18 pounds, depending on sex and individual growth patterns. The World Health Organization places the average (50th percentile) weight for a 5-month-old girl at 6.9 kg, or about 15.2 pounds. Boys tend to be slightly heavier at this age. But averages only tell part of the story. What matters most is that your baby is gaining weight consistently over time, not where they land on a single weigh-in.
Average Weight at 5 Months
The WHO growth standards, which are based on healthy breastfed infants from six countries, provide percentile ranges that pediatricians use worldwide. For 5-month-old girls:
- 5th percentile: 5.6 kg (about 12.3 lbs)
- 50th percentile: 6.9 kg (about 15.2 lbs)
- 95th percentile: 8.4 kg (about 18.5 lbs)
Boys at 5 months generally weigh about half a pound to a pound more than girls at the same percentile. A baby in the 5th percentile is not automatically underweight, just as a baby in the 95th percentile is not automatically overweight. Percentiles describe where your baby falls relative to other babies of the same age and sex. A baby who has tracked along the 15th percentile since birth is growing normally. A baby who drops from the 60th to the 15th over a couple of months may need a closer look.
How Fast Babies Gain Weight at This Age
Between 4 and 6 months, most babies gain about 1 to 1.25 pounds per month, according to Children’s Hospital of Philadelphia. That works out to roughly 4 to 5 ounces per week. This is noticeably slower than the first three months of life, when weekly gains of 5 to 7 ounces are common. The slowdown is normal and expected.
A commonly cited milestone is that babies double their birth weight by around 4 to 5 months. If your baby was born at 7 pounds, you’d expect them to be somewhere near 14 pounds by now. Premature babies or those with a lower birth weight may hit this milestone on a slightly different timeline, and that’s fine as long as the overall trend is upward and steady.
Breastfed vs. Formula-Fed Growth Patterns
Breastfed and formula-fed babies grow differently, and this becomes more noticeable right around the 5-month mark. The CDC notes that formula-fed infants typically gain weight more quickly after about 3 months of age, while healthy breastfed infants tend to put on weight more slowly throughout the first year. These differences persist even after babies start eating solid foods.
This matters because the growth chart your pediatrician uses can influence how your baby’s weight is interpreted. The WHO charts, which are based on breastfed infants, are recommended for all children under 2 in the United States. If your breastfed baby looks like they’re “falling behind” on an older CDC chart designed for a mixed-feeding population, it may simply reflect the normal, slightly leaner growth pattern of breastfed babies. Length (height) growth, interestingly, is similar regardless of feeding method.
Why a Single Number Doesn’t Tell You Much
Pediatricians don’t diagnose a growth problem from one weigh-in. What they’re looking for is the trend. A baby who has always been on the smaller side and continues to gain weight steadily is thriving. The concern arises when a baby’s weight curve flattens or drops across percentile lines over multiple visits. This pattern, sometimes called failure to thrive, reflects insufficient weight gain over time rather than a specific number on the scale.
Several things can temporarily slow weight gain at 5 months: a bout of illness, a growth spurt where length increases before weight catches up, teething discomfort that reduces feeding, or simply normal week-to-week variation. One slow week or even one slow month usually isn’t a concern. A persistent pattern of poor gain over two or three months is worth investigating.
Feeding and Nutrition at 5 Months
At 5 months, breast milk or formula remains your baby’s primary source of nutrition. The American Academy of Pediatrics recommends introducing solid foods around 6 months of age, not earlier. Starting solids before 4 months is associated with increased weight gain and higher rates of obesity later in childhood and into adulthood. Between 4 and 6 months is a gray zone where some pediatricians may give the green light based on developmental readiness (sitting with support, showing interest in food, loss of the tongue-thrust reflex), but there’s no nutritional need to rush.
Most 5-month-olds take in about 24 to 32 ounces of breast milk or formula per day, spread across 4 to 6 feedings. If your baby seems hungry after finishing a bottle or wants to nurse more frequently, it may be a growth spurt rather than a signal to start solids. These spurts are common around 4 and 6 months and typically resolve within a few days.
Signs Your Baby’s Weight May Need Attention
Rather than fixating on a target number, watch for these patterns that suggest your baby may not be getting enough nutrition:
- Fewer than 4 to 6 wet diapers per day, which can indicate insufficient fluid intake
- A noticeable drop across two or more percentile lines on the growth chart over consecutive visits
- Lethargy or poor feeding, where your baby seems too tired to finish meals regularly
- No weight gain at all over a period of several weeks
Keep in mind that babies don’t gain weight in a perfectly linear fashion. A weigh-in right after a big feeding versus right after a diaper change can differ by several ounces. Home scales are also less reliable than the calibrated scales at your pediatrician’s office, so try not to weigh your baby obsessively between visits. The well-child checkup schedule at this age (typically at 4 months and 6 months) is designed to catch problems early while avoiding unnecessary worry from day-to-day fluctuations.