Baby Weight Percentiles Explained: What the Numbers Mean (2026)

What Is a Weight Percentile?

A percentile tells you how your baby’s weight compares to other babies of the same age and sex. A baby at the 60th percentile weighs more than 60% of babies their age — and less than the other 40%. That’s it. There is nothing magical about the 50th percentile.

This is where parents often get tripped up. Percentiles feel like test scores. They’re not. A baby who has always tracked at the 15th percentile is growing perfectly. What pediatricians actually watch for is consistency — does the baby stay on their curve, or do they cross major percentile lines between visits?

According to the American Academy of Pediatrics, healthy babies can range from the 3rd to the 97th percentile on growth charts. Falling anywhere in that range is considered normal. The 3rd percentile means only 3% of same-age babies weigh less — and that can be perfectly healthy.

CDC vs WHO Growth Charts: Which One Applies?

Two sets of charts are commonly used in the United States, and they measure slightly different things.

WHO Growth Charts (0–24 months) were developed from the WHO Multicentre Growth Reference Study (MGRS, 2006) — data collected from children raised under optimal conditions in 6 countries (Brazil, Ghana, India, Norway, Oman, and the United States). All children in the study were breastfed, born into non-smoking households, and had access to good nutrition and healthcare. WHO charts represent prescriptive growth: how babies should grow under ideal circumstances.

CDC Growth Charts (2–20 years) are based on a broader U.S. population sample and are descriptive: they show how American children actually grew, regardless of feeding method or health conditions. The CDC explicitly recommends using WHO charts for infants and toddlers aged 0–24 months and CDC charts for children 2 years and older.

One practical implication: breastfed babies often appear to “fall off” the growth curve around 3–6 months when plotted on CDC charts. This is because the original CDC reference data skewed toward formula-fed infants, who tend to gain weight faster in early infancy. The WHO charts better reflect normal growth for breastfed babies. If your exclusively breastfed baby seems to be dropping percentiles, ask your doctor which chart they’re using.

Average Baby Weight by Age: CDC 50th Percentile Reference Table

The following table shows approximate 50th percentile weights from CDC growth charts. Remember: the 50th percentile is the median, not a goal. Half of all healthy babies weigh less.

Source: CDC Clinical Growth Charts (Kuczmarski et al., 2000), 50th percentile approximations.

According to the CDC’s National Center for Health Statistics (2024), the average birth weight for full-term U.S. babies is approximately 7.5 lbs (3.4 kg). Most full-term newborns fall between 5.5 lbs and 10 lbs at birth.

Growth Velocity: How Much Should a Baby Gain Per Week?

Absolute weight at any given visit matters less than the rate of growth over time. Pediatricians use growth velocity — weight gained per unit of time — to assess whether a baby is thriving.

General guidelines for healthy weight gain:

• 0–3 months: ~5–7 oz (140–200g) per week
• 3–6 months: ~4–5 oz (110–140g) per week
• 6–12 months: ~2–3 oz (56–85g) per week
• 12–24 months: ~1–2 lbs total per month (growth slows significantly)

Newborns typically lose 7–10% of their birth weight in the first few days — this is normal and expected. Most regain their birth weight by 10–14 days. If a baby hasn’t returned to birth weight by 2 weeks, that warrants a call to the pediatrician.

Breastfed babies often gain weight more slowly than formula-fed babies from 3–12 months. This difference is normal and expected, as noted in guidance from both the WHO and the American Academy of Pediatrics. It’s one reason the WHO charts — calibrated on breastfed infants — are preferred for the 0–24 month range.

What Percentile Crossing Actually Means

Some percentile movement is normal, especially in the first few weeks. Newborns often shift percentiles as their weight stabilizes after birth. Genetics play a big role too — a baby born to two smaller parents may naturally track lower on population-based charts, which reflects healthy variation rather than a problem.

The signal that matters: a sustained drop of more than 2 major percentile lines (e.g., from the 75th to the 25th, or from the 50th to the 10th) across multiple visits. According to research published in American Family Physician, this pattern warrants evaluation for potential causes like feeding difficulties, underlying illness, or inadequate caloric intake.

Crossing upward through percentiles can also warrant attention. Rapid weight gain — especially after 6 months — may reflect overfeeding, and a pediatrician can help assess whether intake is appropriate.

Factors That Influence Baby Weight

Growth charts are population tools. Individual variation is enormous and influenced by:

• Genetics: Parents’ build and height are among the strongest predictors of how a child will grow.
• Gestational age: Premature babies are plotted on corrected age charts for the first 2–3 years. A baby born at 32 weeks who is now 6 months old should be compared to 4-month norms (6 months minus 2 months of prematurity).
• Feeding method: Formula-fed infants typically gain weight faster in early infancy than breastfed infants.
• Birth order: Firstborn babies sometimes trend slightly smaller than later siblings.
• Illness: Acute illness can temporarily slow weight gain, followed by catch-up growth.

When to Talk to Your Pediatrician

Growth charts are screening tools, not diagnostic tests. Use them to notice trends, not to panic over a single data point. That said, contact your pediatrician if:

• Your baby drops more than 2 major percentile lines between visits
• Your baby falls below the 3rd percentile or rises above the 97th
• Your newborn hasn’t regained birth weight by 2 weeks
• You notice your baby seems lethargic, refusing feeds, or has fewer wet diapers than expected
• You’re breastfeeding and have concerns about supply or latch

Your pediatrician will look at weight in context with length and head circumference — proportional growth across all three measures is often more reassuring than any single number.

Frequently Asked Questions

What is a healthy weight percentile for a baby?

Any percentile between the 3rd and 97th is considered within the normal range, according to the American Academy of Pediatrics. A baby at the 10th percentile is not underweight, and a baby at the 90th percentile is not overweight. What matters most is that your baby follows a consistent growth curve over time, not where they land on any single visit.

Is the 25th percentile small for a baby?

No. The 25th percentile is completely normal. It simply means your baby weighs more than 25% of babies their age and less than 75%. Percentiles describe a distribution, not a standard to meet. A baby consistently tracking at the 25th percentile is growing just as expected as one at the 75th.

What is the average weight of a 6-month-old baby?

According to CDC growth charts, the average (50th percentile) weight for a 6-month-old girl is approximately 16.1 lbs (7.3 kg) and for a 6-month-old boy is approximately 17.5 lbs (7.9 kg). Healthy 6-month-olds can range from about 13 to 21 lbs depending on where they fall on the growth curve.

When should I be concerned about my baby’s weight?

Talk to your pediatrician if your baby drops more than 2 major percentile lines across multiple visits, falls below the 3rd percentile or above the 97th, is not regaining birth weight by 2 weeks of age, or seems to be losing weight after the normal newborn weight loss window. A single low reading is rarely cause for alarm — trends over time are what matter.

What is the difference between CDC and WHO growth charts?

WHO growth charts (0–24 months) are based on children raised under optimal conditions — breastfed, non-smoking households, good nutrition — across 6 countries. They represent how babies shouldgrow under ideal circumstances. CDC charts are based on a broader U.S. population sample and describe how babies actually grew. The CDC recommends using WHO charts for infants 0–24 months and CDC charts for children 2 and older.

How much weight should a newborn gain per week?

After the normal weight loss in the first few days (up to 7–10% of birth weight), newborns typically regain their birth weight by 10–14 days. From there, babies gain roughly 5–7 oz (140–200g) per week for the first 3 months. Growth velocity then slows: about 4–5 oz per week from 3–6 months, and 2–3 oz per week from 6–12 months. These are averages — short growth spurts and plateaus are both normal.