Average Baby Weight For Age: Complete Month-by-Month Guide With Charts

Parents constantly wonder whether their baby's weight is normal. The average baby weight for age provides a baseline to understand typical growth patterns, though healthy babies exist across a wide range. This guide breaks down expected weight milestones from birth through age 2, explains what influences baby weight, and clarifies when weight patterns require medical attention.

Average Baby Weight at Birth

Full-term newborns (37-40 weeks gestation) average between 6.5 and 9.5 pounds, with most falling around 7.5 pounds. Birth weight depends heavily on several factors: genetics, maternal nutrition during pregnancy, gestational diabetes, and whether the baby is a boy or girl.

Average birth weight by sex:

Low birth weight (under 5.5 lbs) and high birth weight (over 8.8 lbs) both carry health implications and require monitoring, though many of these babies grow typically afterward.

Average Baby Weight: First 6 Months

The first 6 months represent the most rapid growth period of human life. Babies typically double their birth weight by 5 months and gain 5-7 ounces per week during months 1-3.

Month-by-Month Weight Averages

Growth velocity (rate of weight gain) naturally slows after month 3. A baby gaining 180g per week at 2 months who slows to 120g per week at 5 months is following the normal pattern.

What Affects Weight in Early Months

Feeding method: Breastfed and formula-fed babies grow differently. Formula-fed babies often gain weight slightly faster in early months, while breastfed babies' weight gain aligns more closely with WHO standards (based on breastfed babies from optimal conditions).

Feeding frequency: Newborns need 8-12 feedings per 24 hours. Babies who feed less frequently may gain weight more slowly.

Medical conditions: Reflux, tongue ties, milk protein allergies, and metabolic disorders can all impact weight gain.

Average Baby Weight: 6 to 12 Months

Growth continues but at a notably slower pace. Babies triple their birth weight by their first birthday and gain approximately 3 ounces per week during this period.

During these months, babies become increasingly mobile. Crawling, standing, and early walking burn significant calories, which can temporarily slow weight gain. This is normal. As long as the baby maintains their growth curve, the slower gain reflects increased activity rather than inadequate nutrition.

Average Toddler Weight: 12 to 24 Months

After the first birthday, weight gain slows dramatically to approximately 3-5 pounds per year. Toddlers slim down as they become more active, transitioning from baby fat to leaner muscle tone.

Toddlers often move down 1-2 percentile curves during this period as their body composition changes. A baby at the 75th percentile at 12 months who drops to the 50th percentile by 18 months isn't necessarily losing weight, they are growing into a leaner build typical for active toddlers.

Understanding Percentiles vs. Averages

The 50th percentile represents the median weight where half of babies weigh more and half weigh less. It is the average. But the 50th percentile is not the goal or the "correct" weight.

What percentiles actually mean:

• 5th percentile: 95% of babies weigh more (smaller than average but often healthy)
• 25th percentile: 75% of babies weigh more
• 50th percentile: The median average
• 75th percentile: 25% of babies weigh more
• 95th percentile: Only 5% of babies weigh more (larger than average but often healthy)

A baby consistently at the 10th percentile who grows steadily along that curve is healthy. A baby jumping from the 75th to the 25th percentile over 2-3 months needs evaluation, even though 25th percentile is "normal."

Factors That Influence Baby Weight

Genetics

Tall parents tend to have bigger babies. Short parents tend to have smaller babies. A baby's genetic potential often becomes apparent by 6-12 months as they find their natural growth curve.

Sex

Boys average 2-3% heavier than girls at every age milestone. This difference is biological and consistent across populations.

Feeding Method

Breastfed babies gain weight more slowly after month 3-4 compared to formula-fed babies. WHO growth charts (the international standard) are based on breastfed babies, representing optimal growth.

Prematurity

Premature babies use corrected age (gestational age adjusted for how early they were born) on growth charts until age 2. A baby born 8 weeks early at chronological age 6 months plots at 4 months corrected age.

Medical Conditions

Conditions affecting nutrient absorption, hormone levels, or metabolism can impact weight gain. Diagnosed conditions require specialized growth monitoring.

When Average Baby Weight Isn't Average

Some babies are naturally large or small but grow perfectly well. The key is distinguishing normal variation from problematic patterns.

Healthy growth indicators:

• Steady weight gain over time
• Maintaining a consistent percentile curve
• Meeting developmental milestones
• Good feeding (breast/bottle) and normal output (wet diapers, stools)
• Active, alert, and responsive

Concerning patterns requiring evaluation:

• Crossing 2+ percentile curves downward
• No weight gain for 1 month (under 6 months) or 2 months (over 6 months)
• Weight loss after regaining birth weight
• Consistently below 3rd percentile or above 97th percentile
• Significant disparity between weight and length percentiles

Boy vs. Girl Weight Differences

Boys consistently weigh more than girls at every age, though the difference is modest (about 5-8 ounces on average). This reflects biological differences in muscle mass and body composition.

Comparison at key milestones:

Using gender-specific growth charts ensures accurate comparisons. A girl plotted on a boys' chart appears smaller than she actually is relative to other girls.

Tracking Your Baby's Weight at Home

Home tracking between pediatrician visits helps identify trends early and provides reassurance. Weekly weigh-ins work well for babies under 6 months. Monthly works for older babies.

Bring your tracking logs to pediatrician appointments. Weeks of data reveal trends that single measurements miss.

What to Do If Your Baby's Weight Is Off Track

If you notice your baby has lost weight, stopped gaining weight, or crossed 2+ percentile curves, contact your pediatrician. Early intervention is most effective.

Your doctor will:

• Review feeding history (frequency, volume, techniques)
• Examine your baby for signs of illness
• Evaluate developmental milestones
• Consider tests if needed (metabolic screening, food sensitivities)
• Recommend interventions (feeding changes, specialist referrals)

Weight issues often have straightforward solutions like adjusting feeding frequency, addressing latching problems, or treating reflux.

The Bottom Line on Average Baby Weight for Age

Average baby weight for age provides a reference point, not a target. Healthy babies exist across the entire range of percentiles from 5th to 95th. What matters is steady growth along a consistent curve over time.

Track your baby's weight monthly, plot it on growth charts (WHO for ages 0-24 months), calculate growth velocity, and compare weight percentile to length percentile. Babies who track steadily, feed well, develop typically, and act healthy are thriving regardless of whether they are at the 10th or 90th percentile.

Bring concerns to your pediatrician promptly. Most weight issues have simple solutions when caught early. Trust your instincts, track consistently, and remember that every baby grows at their own pace within the broad range of normal.

References

1. World Health Organization. WHO Child Growth Standards. Available at: https://www.who.int/tools/child-growth-standards
2. Centers for Disease Control and Prevention. Clinical Growth Charts. Available at: https://www.cdc.gov/growthcharts/clinical_charts.htm
3. American Academy of Pediatrics. Healthy Children - Growth Charts. Available at: https://www.healthychildren.org/English/health-issues/conditions/Glands-Growth-Disorders/Pages/Growth-Charts-By-the-Numbers.aspx