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Baby Weight Percentile Calculator: Is My Baby Growing Normally?

Enter your baby's age, weight, and sex to see an estimated weight percentile based on CDC growth chart values. Remember: any consistent curve is healthy, and percentile number is just one piece of the picture.

Baby Weight Percentile Calculator

Enter your baby's age, sex, and weight to estimate their percentile on CDC growth charts.

What Does Percentile Actually Mean?

A weight percentile tells you how your baby's weight compares to other babies of the same age and sex in the reference population. It is a comparison tool, not a report card.

Example: What the 40th percentile means

If your baby is at the 40th percentile for weight at 6 months, their weight is higher than 40% of 6-month-old babies of the same sex in the reference population, and lower than 60%. They are right in the middle of the range, which is completely normal.

Below 5th percentile

May indicate concern. Pediatrician will investigate trends.

5th - 95th percentile

Normal, healthy range. Any consistent curve here is good.

Above 95th percentile

May warrant monitoring. Pediatrician reviews full picture.

Average Baby Weight by Age

50th percentile (average) weights for boys and girls from birth to 24 months:

AgeAverage Boy WeightAverage Girl Weight
Birth7.8 lbs (3.5 kg)7.5 lbs (3.4 kg)
1 month9.9 lbs (4.5 kg)9.2 lbs (4.2 kg)
2 months12.3 lbs (5.6 kg)11.3 lbs (5.1 kg)
4 months15.4 lbs (7.0 kg)14.1 lbs (6.4 kg)
6 months17.4 lbs (7.9 kg)16.1 lbs (7.3 kg)
9 months20.1 lbs (9.1 kg)18.8 lbs (8.5 kg)
12 months22.0 lbs (10.0 kg)20.7 lbs (9.4 kg)
18 months24.7 lbs (11.2 kg)23.4 lbs (10.6 kg)
24 months27.5 lbs (12.5 kg)26.5 lbs (12.0 kg)

50th percentile values from CDC growth charts 2000. Remember: these are averages. Any consistent growth trend across the 5th-95th percentile range is healthy.

CDC vs. WHO Growth Charts: What Is the Difference?

CDC Growth Charts (2000)
  • Developed using a US representative sample
  • Includes both breastfed and formula-fed babies
  • Commonly used in US pediatric offices
  • Less ideal as a standard for breastfed babies
  • Used in this calculator for 0-24 months
WHO Growth Charts (2006)
  • International sample from 6 countries
  • Based on optimally-fed, non-smoking households
  • Considered the gold standard for healthy infant growth
  • AAP recommends for infants under 2 years
  • Slightly different reference values, especially for breastfed babies

Signs Your Baby Is Growing Well

Weight percentile is one of many indicators. These signs together paint a much clearer picture of healthy growth:

📈

Following a consistent percentile curve across multiple visits (even if low or high)

💧

6 or more wet diapers per day in the first months

😄

Alert, interactive, and content during awake periods

🍼

Feeding well and seeming satisfied after meals

👶

Gaining length and head circumference appropriately

🏃

Reaching developmental milestones for their age

🌙

Has some predictable sleep patterns (even if still waking)

🔄

Regular bowel movements (frequency varies widely and is normal)

When to Talk to Your Pediatrician

Bring up at your next well-child visit if:

  • Baby drops two or more major percentile lines between visits
  • Weight consistently below the 5th percentile
  • Baby seems constantly hungry despite frequent feedings
  • Fewer than 6 wet diapers per day after the first week
  • Baby is not regaining birth weight by 2 weeks
  • You feel worried about your baby's growth, regardless of numbers

Your pediatrician is the best resource for growth concerns. They have the full picture of your baby's health history, feeding patterns, and family genetics that no online calculator can replicate.

Frequently Asked Questions

What does baby weight percentile mean?
A percentile tells you how your baby's weight compares to other babies of the same age and sex. If your baby is at the 40th percentile, they weigh more than 40% of babies their age, and less than 60%. It is not a grade or ranking, just a comparison point.
What is a healthy weight percentile for a baby?
There is no single healthy percentile. Any percentile from the 5th to the 95th is considered within the normal range. What matters most is that your baby follows a consistent growth curve over time, not that they hit a specific number.
Should I worry if my baby is in a low percentile?
Not necessarily. A baby who has always been at the 10th percentile and continues to follow that curve is growing normally for them. Concern arises when a baby drops significantly across percentile lines, which is why your pediatrician tracks trends over multiple visits.
What is the difference between CDC and WHO growth charts?
The WHO charts (2006) are based on an international sample of optimally-fed children and are considered the gold standard for infants 0-2 years. CDC charts (2000) are based on a US representative sample. The AAP recommends using WHO charts for infants under 2 years. Both are commonly used in pediatric practice.
How much should a baby gain per week?
Typical weight gain: Newborn to 4 months: about 5-7 oz per week. 4-6 months: about 3-5 oz per week. 6-12 months: about 1-3 oz per week. Weight gain naturally slows as babies grow. Your pediatrician will track if the rate is appropriate.
Why do breastfed babies sometimes fall on lower percentiles?
Breastfed babies often follow a slightly different growth curve than formula-fed babies, particularly in the second half of the first year. The WHO charts were developed using breastfed babies and are the more appropriate reference for breastfed infants.
My baby was 90th percentile at birth, now 50th at 6 months. Should I worry?
Some natural settling of percentiles in the first few months is normal, especially for large newborns. However, a significant drop across percentile lines should be discussed with your pediatrician. They will look at the full clinical picture, not just one number.
When do babies double their birth weight?
Most babies double their birth weight by 4-5 months. Tripling birth weight typically happens around 12 months. These are average milestones, and there is a range of normal.
What if my baby is above the 97th percentile?
Being above the 97th percentile warrants a conversation with your pediatrician, but does not automatically mean something is wrong. Your doctor will look at your baby's full growth pattern, feeding habits, family history, and other factors.
Does this calculator work for premature babies?
For premature babies, always use corrected age (adjusted for prematurity) when looking up percentiles, not actual age. Use our Adjusted Age Calculator first to find your baby's corrected age, then input that into this calculator.

Medical Disclaimer: This calculator uses approximate CDC growth chart values for educational purposes only. Percentile results are estimates and are not a substitute for professional medical evaluation. Always discuss your baby's growth with your pediatrician.

Understanding Baby Growth Charts: A Complete Guide

Growth charts are one of the most powerful tools pediatricians use to monitor infant health. Understanding how to read them helps you have more informed conversations with your baby's doctor.

What Percentile Means

A baby at the 60th percentile for weight weighs more than 60% of babies the same age. There is no 'ideal' percentile, what matters is that your baby grows consistently along their own curve over time.

Consistent Growth Matters More

A drop from the 80th to the 20th percentile is more concerning than being consistently on the 15th. Steady growth along a consistent curve, even a low one, indicates a healthy baby.

WHO vs. CDC Charts

The AAP recommends using WHO charts (2006) for all babies under 24 months because they are based on optimally-fed children worldwide. CDC charts (2000) are used for children 2 years and older.

Weight, Length, and Head Circumference

Pediatricians plot three measurements: weight, length, and head circumference. Each tells a different story about growth. Head circumference reflects brain growth; weight reflects nutrition; length reflects skeletal growth.

Breastfed vs. Formula-Fed Growth

Breastfed babies tend to grow rapidly in the first 3 months, then more slowly from 3–6 months. This is normal. The WHO charts were developed using breastfed babies as the gold standard.

When to Discuss with a Pediatrician

Alert your pediatrician if your baby crosses two major percentile lines (e.g., drops from 50th to below 10th), has consistently low or high percentiles with symptoms, or you are concerned about growth for any reason.

Average Baby Weight and Length by Month

These are the 50th percentile (median) values from WHO growth standards for healthy, full-term infants. Your baby does not need to match these exactly, use as a general reference only.

AgeBoys WeightGirls WeightBoys LengthGirls Length
Birth7.5 lbs (3.4 kg)7.3 lbs (3.3 kg)19.7 in (50.0 cm)19.4 in (49.1 cm)
1 Month9.9 lbs (4.5 kg)9.2 lbs (4.2 kg)21.2 in (53.8 cm)20.7 in (52.6 cm)
2 Months12.3 lbs (5.6 kg)11.5 lbs (5.2 kg)22.9 in (58.1 cm)22.4 in (56.8 cm)
4 Months15.4 lbs (7.0 kg)14.1 lbs (6.4 kg)24.9 in (63.2 cm)24.2 in (61.5 cm)
6 Months17.5 lbs (7.9 kg)16.1 lbs (7.3 kg)26.6 in (67.5 cm)25.8 in (65.5 cm)
9 Months20.1 lbs (9.1 kg)18.5 lbs (8.4 kg)28.3 in (71.9 cm)27.6 in (70.1 cm)
12 Months22.0 lbs (10.0 kg)20.4 lbs (9.3 kg)29.8 in (75.8 cm)29.1 in (74.0 cm)

Source: WHO Child Growth Standards (2006), 50th percentile values. These are averages, healthy babies span a wide range around these values.

Track Your Baby's Growth with Confidence

Complement this calculator with our free growth guides and feeding tools.

Growth and Milestone GuidesAdjusted Age CalculatorFeeding CalculatorSolid Food Readiness