The average 5-month-old weighs about 15 to 16 pounds, though healthy babies at this age can range anywhere from around 12 to 19 pounds depending on sex, birth weight, and feeding method. Most babies have doubled their birth weight by this point, which is one of the key milestones pediatricians look for.
Average Weight by Sex
Boys and girls follow slightly different growth curves. Based on the World Health Organization growth standards used by pediatricians in the United States, the 50th percentile (the true statistical middle) for a 5-month-old boy is about 16.1 pounds. For a 5-month-old girl, it’s about 14.8 pounds.
Those are midpoints, not targets. A baby at the 25th percentile is just as healthy as one at the 75th percentile, as long as they’re growing consistently along their own curve. The normal range spans roughly 12.5 to 19 pounds for boys and 11.5 to 17.5 pounds for girls at this age.
How Fast Weight Gain Happens at This Age
Between 4 and 6 months, babies typically gain about 1 to 1.25 pounds per month. That’s slower than the newborn phase, when many babies pack on about an ounce a day. By around 4 months, daily weight gain drops to about 20 grams (roughly two-thirds of an ounce), and it continues to slow as babies approach 6 months.
This deceleration is completely normal. Babies grow fastest in their first three months, then gradually shift more energy toward motor development, rolling, reaching, and preparing to sit up. If your baby seems to be gaining less than before, that expected slowdown is likely the reason.
The Birth Weight Connection
A baby’s weight at 5 months is strongly tied to how much they weighed at birth. A baby born at 6 pounds will likely weigh less at 5 months than one born at 9 pounds, even if both are perfectly healthy and growing well. The doubling-of-birth-weight milestone captures this nicely: a 7-pound newborn reaching about 14 pounds by 5 months is right on track, while a 9-pound newborn might need to hit closer to 18 pounds to meet the same benchmark.
Premature babies follow a different trajectory entirely. Pediatricians use their “corrected age” (calculated from their due date, not their birth date) when plotting growth. A baby born four weeks early and now 5 months old would be compared against the growth chart for a 4-month-old.
Breastfed vs. Formula-Fed Babies
Breastfed and formula-fed infants grow at noticeably different rates, and those differences are well-documented. After about 3 months of age, formula-fed babies typically gain weight faster than breastfed babies. This pattern continues even after solid foods enter the picture.
This does not mean breastfed babies are underfed. The WHO growth charts, which are now the standard for children under 2 in the U.S., were built primarily from data on breastfed infants. If your pediatrician is using older CDC charts, a breastfed baby might appear to “fall off” their curve when they’re actually growing normally. It’s worth asking which chart your doctor uses.
How Much a 5-Month-Old Eats
At this age, breast milk or formula is still the sole source of nutrition for most babies. The general guideline for formula-fed infants is about 2.5 ounces per day for every pound of body weight. So a 15-pound baby would need roughly 37.5 ounces, though most babies cap out at around 32 ounces in a 24-hour period. Babies are good at self-regulating their intake, so daily amounts will fluctuate.
Breastfed babies are harder to measure in ounces, but they typically nurse 5 to 7 times per day at this stage. Adequate wet diapers (six or more in 24 hours) and steady weight gain at checkups are the most reliable signs that a breastfed baby is getting enough.
When Weight Gain Is a Concern
Pediatricians aren’t concerned about a single weight measurement. What matters is the pattern over time. A baby who has been tracking along the 20th percentile since birth is growing well. A baby who drops from the 60th percentile to the 15th over two or three visits may need evaluation, because that kind of decline in growth velocity can signal a feeding issue, digestive problem, or other underlying cause.
There’s no single number that defines “too light” or “too heavy” at 5 months. The key question is whether your baby is following a consistent curve on their growth chart. Pediatricians typically plot weight at every well-child visit (usually at 4 months and 6 months around this age), so trends become visible quickly. If your baby is alert, feeding well, producing plenty of wet diapers, and hitting developmental milestones like reaching for objects and tracking faces, those are strong signs that growth is on track regardless of the exact number on the scale.