A 5-month-old baby typically weighs between 12.1 and 18.5 pounds (5.5 to 8.4 kg), depending on sex and individual growth pattern. The average sits right around 15 pounds for girls and a bit higher for boys. But the number on the scale matters less than whether your baby is growing consistently along their own curve.
Average Weight at 5 Months
The World Health Organization growth standards, which the CDC recommends for all U.S. infants from birth to age 2, place the 50th percentile for 5-month-old girls at 6.9 kg (about 15.2 pounds). Boys tend to run slightly heavier at the same age, with a 50th percentile around 7.5 kg (16.5 pounds).
Percentiles give you context for where your baby falls relative to other healthy infants worldwide. A baby at the 5th percentile for girls weighs about 5.6 kg (12.3 pounds), while a baby at the 95th percentile weighs roughly 8.4 kg (18.5 pounds). Both are normal. A baby who has tracked along the 20th percentile since birth is growing exactly as expected, even though they weigh less than most babies their age. What pediatricians watch for is a baby who drops across two or more percentile lines over time, which can signal a feeding or health issue worth investigating.
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’s noticeably slower than the rapid gains of the first three months, when some babies pack on close to 2 pounds per month. This gradual slowdown is completely normal and reflects a shift toward more active development: rolling, reaching, and building muscle instead of simply adding body fat.
A helpful benchmark is that most healthy, full-term babies double their birth weight by around 4 months. So a baby born at 7.5 pounds would be expected to weigh roughly 15 pounds by month 4 or 5. If your baby was smaller or larger at birth, their 5-month weight should scale accordingly.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed babies follow different weight trajectories, and knowing this can save you unnecessary worry. Healthy breastfed infants typically gain weight more slowly than formula-fed infants, with the difference becoming more noticeable after about 3 months. Formula-fed babies tend to put on weight faster from that point forward, and the gap continues even after solid foods enter the picture.
Importantly, both groups grow in length at similar rates. The difference is mostly in fat accumulation, not overall development. The WHO growth charts were built from data on breastfed infants, so if your baby is breastfed and tracking along a lower percentile, they may be right on target. Older growth charts based primarily on formula-fed babies can make breastfed infants look like they’re falling behind when they’re not.
What Matters More Than the Number
Your pediatrician plots your baby’s weight at each visit not to compare them to other babies, but to track their individual trend line. A baby who consistently follows the 25th percentile is thriving. A baby who was at the 75th percentile and has dropped to the 25th over two visits deserves a closer look, even though 25th percentile is technically “normal.”
Other signs that your baby is getting enough nutrition at 5 months include producing at least 5 to 6 wet diapers a day, seeming satisfied after feedings, staying alert and active during wake windows, and meeting motor milestones like reaching for objects and beginning to roll. Weight is one data point in a bigger picture.
Adjusted Age for Premature Babies
If your baby was born early, their weight expectations shift. Pediatricians use “corrected age,” which is your baby’s age minus the number of weeks they arrived before their due date, when plotting growth. A baby born 8 weeks early who is now 5 months old would be evaluated as a 3-month-old on the growth chart. This correction is standard practice until age 2, because premature infants need that extra time to catch up to full-term growth curves. Specialized preemie growth charts are also used in the early months before transitioning to the standard WHO charts.
So if your 5-month-old was premature and seems small compared to the ranges above, their corrected-age weight may be perfectly appropriate. Your pediatrician can confirm whether their growth trajectory looks healthy given their adjusted timeline.