Most 5-month-old babies weigh between about 12 and 18.5 pounds (5.4 to 8.4 kg), with the average falling around 15 pounds for girls and slightly higher for boys. That’s a wide range, and where your baby falls within it depends on birth weight, feeding method, genetics, and overall health. What matters most isn’t hitting one specific number but following a consistent growth curve over time.
Average Weight for 5-Month-Old Girls and Boys
The World Health Organization growth standards, which pediatricians use as the primary reference for infant growth, put the 50th percentile weight for 5-month-old girls at 6.9 kg (about 15.2 pounds). A girl at the 5th percentile weighs around 5.6 kg (12.3 pounds), while one at the 95th percentile weighs about 8.4 kg (18.5 pounds). Boys tend to run slightly heavier at every percentile, with the 50th percentile typically falling around 7.5 kg (16.5 pounds).
These percentiles aren’t pass/fail markers. A baby at the 15th percentile who has tracked along that curve since birth is growing perfectly normally. Pediatricians look for babies to stay on or near the same percentile line from visit to visit, rather than aiming for a particular number.
How Fast Babies Gain Weight at This Age
Weight gain slows noticeably between 4 and 6 months compared to the newborn period. In the first few months of life, babies gain roughly 1 ounce (28 grams) per day. By 4 months that drops to about 20 grams per day, and by 6 months many babies are gaining 10 grams or less daily. According to Children’s Hospital of Philadelphia, the typical weight gain between 4 and 6 months averages 1 to 1.25 pounds per month.
This slowdown is completely normal and catches many parents off guard. A baby who seemed to pack on weight effortlessly in the early weeks may now appear to plateau, especially if they’ve also become more active, rolling over and spending energy on new movements. The key number to watch is the overall trend across several weeks, not day-to-day fluctuations.
Breastfed vs. Formula-Fed Babies
Feeding method has a real effect on weight gain patterns at this age. Breastfed babies typically gain weight more slowly than formula-fed babies after about 3 months. The CDC notes that this difference persists even after solid foods are introduced later on. Both groups grow in length at similar rates, so the difference is specifically in weight, not overall size.
This matters because growth charts based on formula-fed populations can make a healthy breastfed baby look like they’re falling behind. That’s one reason the WHO charts, which are based on breastfed infants, became the standard for children under 2 in the United States. If your pediatrician uses the WHO charts (most do for this age group), a breastfed baby’s slightly leaner build is already accounted for.
Growth Spurts Around 5 Months
Typical infant growth spurts occur at 2 to 3 weeks, 6 weeks, 3 months, 6 months, and 9 months. Five months falls between two common spurt windows, but every baby’s timing is different. During a growth spurt, you may notice increased fussiness, a sudden jump in hunger, or your baby wanting to feed more frequently. These episodes are short, usually lasting up to three days in infants, and they can temporarily shift how much your baby eats and gains.
When Weight Gain May Be Too Slow
A baby who drops across two or more percentile lines on their growth chart, or who isn’t gaining any weight over several weeks, may need closer evaluation. Some practical signs that a baby isn’t getting enough nutrition include fewer wet and dirty diapers than usual, dry lips, a sunken soft spot on the head, dark circles around the eyes, and unusual sleepiness.
Breastfed babies at this age should still be nursing about 8 to 12 times in 24 hours. Some babies become “sleepy feeders” who don’t signal hunger often enough on their own. If your baby isn’t cueing to feed at least 8 times a day, you may need to wake them every 2 hours during the day and every 3 to 4 hours at night to ensure adequate intake.
Adjusted Age for Premature Babies
If your baby was born before 37 weeks, the weight ranges above won’t apply directly. Premature infants are tracked using their adjusted age, which is their actual age minus the number of weeks they arrived early. A baby born at 33 weeks who is now 5 months old has an adjusted age of about 3 months, and their weight should be compared to the 3-month standards instead. Pediatricians use specialized preterm growth charts (such as the Fenton chart) until a premature baby’s growth catches up to the standard WHO curves, which often happens within the first two years.
What Matters More Than the Number
Your baby’s single weight measurement at 5 months is far less important than their growth pattern over time. A baby who has consistently tracked the 25th percentile is thriving just as much as one on the 75th. Weight should also be considered alongside length. A long, lean baby at a lower weight percentile may be perfectly proportional, which is why pediatricians check weight-for-length charts in addition to weight-for-age. If your baby is alert, active, producing plenty of wet diapers, and meeting developmental milestones like reaching for objects and rolling, their weight is very likely right where it should be.