CDC Growth Charts · Boys & Girls · 0-24 Months

Baby Weight Percentile Calculator

Find your baby's weight percentile instantly using CDC growth charts. Enter your baby's age, weight, and sex to see where they fall among other babies the same age.

Last updated · Percentiles checked against WHO growth standards via CDC data files

CDC Growth Charts
Boys & Girls
Birth to 24 Months
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Baby Weight Percentile Calculator
WHO growth charts (CDC recommended) · 0 to 24 months
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Enter your baby's age, weight, and sex to find their growth percentile.

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Understanding Baby Growth Percentiles

At 2 months the median weight on the WHO growth charts is 12.3 lb (5.6 kg) for boys and 11.3 lb (5.1 kg) for girls. Enter your baby's age, sex and weight above to get the exact percentile. The calculator uses the WHO standards that CDC recommends for all US children under 2 and the standard LMS method to turn weight into a percentile.

A baby's weight percentile shows how their weight compares to other babies of the same age and sex. A 50th percentile means your baby weighs more than 50% of babies the same age. A wide range is normal: with the WHO charts, CDC uses the 2nd and 98th percentile lines (2.3rd and 97.7th) as screening cutoffs.

Growth trends matter more than a single measurement. A baby consistently at the 20th percentile is growing normally. A baby who drops from the 60th to the 10th percentile over several months warrants discussion with a pediatrician. Your pediatrician tracks weight, length, and head circumference at every well-baby visit.

What is a Normal Percentile?

With the WHO charts, CDC uses the 2nd and 98th percentile lines (2.3rd and 97.7th) as screening cutoffs. There is no 'ideal' percentile: a healthy baby can be at the 10th or the 90th. Below the 2nd percentile line or above the 98th line warrants a closer look, but doesn't automatically indicate a problem.

Growth Trends vs Single Points

A single percentile measurement is less informative than the trend over time. Consistent growth along any percentile curve indicates healthy development. Crossing two major percentile lines up or down (e.g., dropping from 75th to 25th) in a short period is more concerning than absolute position.

Boys vs Girls

Boys and girls have different growth charts because boys are typically slightly heavier at most ages. Using the correct sex is essential for accurate percentile calculation. The CDC provides separate charts, as does the WHO for the first 2 years.

CDC vs WHO Charts

The CDC recommends using WHO growth charts for children under 2 years old in the US (updated 2010 guidance), and CDC charts for ages 2-20. WHO charts are based on children raised under optimal conditions (breastfed, non-smoking household), representing ideal growth rather than national average. This calculator uses the WHO standards, as CDC recommends for babies under 2. At the second birthday US practice switches to the CDC charts, and because the two are built from different groups of children the same child can land a few percentile points apart on the day of the switch. That is a change of chart, not a change in your child, so it is worth asking which chart a number came from before comparing two visits.

Weight Percentiles for Boys, Birth to 24 Months

WHO growth standard, weight-for-age. Values computed from the official WHO LMS parameters.

Age5th percentile50th (median)95th percentile
Birth5.7 lb (2.6 kg)7.4 lb (3.3 kg)9.3 lb (4.2 kg)
1 month7.9 lb (3.6 kg)9.9 lb (4.5 kg)12.2 lb (5.5 kg)
2 months10.0 lb (4.5 kg)12.3 lb (5.6 kg)15.0 lb (6.8 kg)
3 months11.6 lb (5.2 kg)14.1 lb (6.4 kg)17.0 lb (7.7 kg)
4 months12.8 lb (5.8 kg)15.4 lb (7.0 kg)18.5 lb (8.4 kg)
6 months14.6 lb (6.6 kg)17.5 lb (7.9 kg)20.9 lb (9.5 kg)
9 months16.4 lb (7.4 kg)19.6 lb (8.9 kg)23.4 lb (10.6 kg)
12 months17.8 lb (8.1 kg)21.3 lb (9.6 kg)25.4 lb (11.5 kg)
15 months19.0 lb (8.6 kg)22.7 lb (10.3 kg)27.2 lb (12.3 kg)
18 months20.1 lb (9.1 kg)24.1 lb (10.9 kg)28.9 lb (13.1 kg)
24 months22.2 lb (10.1 kg)26.8 lb (12.2 kg)32.3 lb (14.7 kg)

Weight Percentiles for Girls, Birth to 24 Months

Same method, girls' chart. At every age girls' medians run a little below boys'.

Age5th percentile50th (median)95th percentile
Birth5.6 lb (2.5 kg)7.1 lb (3.2 kg)8.9 lb (4.0 kg)
1 month7.3 lb (3.3 kg)9.2 lb (4.2 kg)11.5 lb (5.2 kg)
2 months9.1 lb (4.1 kg)11.3 lb (5.1 kg)14.0 lb (6.3 kg)
3 months10.5 lb (4.7 kg)12.9 lb (5.8 kg)15.8 lb (7.2 kg)
4 months11.5 lb (5.2 kg)14.2 lb (6.4 kg)17.4 lb (7.9 kg)
6 months13.2 lb (6.0 kg)16.1 lb (7.3 kg)19.7 lb (8.9 kg)
9 months14.9 lb (6.8 kg)18.1 lb (8.2 kg)22.2 lb (10.1 kg)
12 months16.2 lb (7.3 kg)19.7 lb (8.9 kg)24.2 lb (11.0 kg)
15 months17.4 lb (7.9 kg)21.2 lb (9.6 kg)26.0 lb (11.8 kg)
18 months18.5 lb (8.4 kg)22.6 lb (10.2 kg)27.8 lb (12.6 kg)
24 months20.8 lb (9.4 kg)25.3 lb (11.5 kg)31.2 lb (14.2 kg)

How the Percentile Is Calculated

WHO publishes three numbers for each month of age and each sex: L (skewness), M (the median weight) and S (spread). The calculator turns your baby's weight W into a z-score with the LMS formula, then converts the z-score to a percentile with the normal distribution:

z = ((W ÷ M)L − 1) ÷ (L × S)

Worked example

A 2-month-old boy weighs 12 lb, which is 5.44 kg. For boys at 2 months WHO gives L = 0.197, M = 5.5675 kg and S = 0.12385. That makes z = −0.18, which is the 43rd percentile: he weighs more than about 43 of every 100 boys his age in the WHO reference group. At 11 lb the same boy would be at the 19th percentile.

Which cutoffs matter

With the WHO charts, CDC recommends the 2.3rd and 97.7th percentiles (drawn as the 2nd and 98th lines) as the screening cutoffs, not the 5th and 95th used on CDC charts for older children. A result outside them is a reason to talk to your pediatrician, not a diagnosis. For babies born early, pediatricians usually plot weight at corrected age (age minus the weeks born early) until about 2 years.

From age 2 the CDC 2000 growth charts take over. For adults, see the BMI calculator.

Method and sources. Percentiles use the WHO Child Growth Standards weight-for-age LMS parameters (birth to 24 months) as published in CDC's WHO growth chart data files, with z = ((W/M)^L minus 1) divided by (L times S) and the standard normal distribution. Table values computed with the same parameters. Chart choice and cutoffs: CDC, Use of World Health Organization and CDC Growth Charts for Children Aged 0 to 59 Months in the United States (MMWR 2010). Well-child visit schedule: AAP Bright Futures. This is information, not a medical assessment; your pediatrician interprets growth over time.
This calculator uses the WHO growth standards recommended by CDC for children under 2, for informational purposes only. Growth assessment requires clinical evaluation by a qualified healthcare provider. Always discuss your baby's growth with your pediatrician.

Frequently Asked Questions

A percentile tells you how your baby's weight compares to other babies of the same age and sex in the reference population. 50th percentile: your baby weighs more than 50% of babies the same age. 75th: weighs more than 75%. 25th: weighs less than 75% but is still completely normal. Most healthy babies sit between the 2nd and 98th percentile lines, the cutoffs CDC recommends with the WHO charts.

On the WHO charts CDC recommends, a weight below the 2.3rd percentile (the 2nd percentile line) is the usual cutoff for low weight-for-age, but context matters enormously. A baby consistently at the 3rd percentile who is alert, feeding well, hitting milestones, and trending along their curve may be perfectly healthy (small parents often have small babies). 'Failure to thrive' is diagnosed based on dropping across percentile lines and clinical assessment, not a single number.

Pediatricians track weight at every well-baby visit: 3-5 days (newborn check), 1 month, 2 months, 4 months, 6 months, 9 months, 12 months, 15 months, 18 months, 2 years, 30 months, then yearly from age 3. Between visits, weight tracking at home is helpful but not necessary if the baby is feeding well, producing wet diapers, and meeting developmental milestones.

Some percentile drop is normal and expected. Many babies are born at a higher-than-genetic percentile due to gestational factors, then drop to their genetic 'true' percentile in the first 3-6 months. Breastfed babies often grow faster than formula-fed in the first 3 months, then slower. If your baby drops significantly (crossing two major percentile lines) without explanation, discuss with your pediatrician.

Median weight at 2 months on the WHO charts: boys 5.6 kg (12.3 lb), girls 5.1 kg (11.3 lb). The 5th to 95th percentile range is 4.5 to 6.8 kg (10.0 to 15.0 lb) for boys and 4.1 to 6.3 kg (9.1 to 14.0 lb) for girls. Babies typically regain birth weight by 10-14 days and gain about 150-200g (5-7 oz) per week in the first 3 months.

Expected weight gain: Birth to 3 months: 150-200g (5-7 oz) per week. 3-6 months: 100-150g (3-5 oz) per week. 6-12 months: 70-90g (2-3 oz) per week. Most babies lose 5-10% of birth weight in the first week (normal), regain it by days 10-14, then gain steadily. Breastfed babies may be slightly slower gainers in months 4-12 compared to formula-fed.

Median birth weight on the WHO growth standard: boys 3.3 kg (7 lb 6 oz), girls 3.2 kg (7 lb 2 oz). Low birth weight is defined as under 2.5 kg (5.5 lbs). Macrosomia (large baby) is typically over 4.0 kg (8.8 lbs). Factors affecting birth weight: gestational age, maternal nutrition, maternal weight and height, multiple gestation, genetic factors.

Discuss with your pediatrician if: baby doesn't regain birth weight by 2 weeks, baby loses more than 10% of birth weight, drops more than two major percentile lines, appears lethargic or unresponsive, is not producing 6+ wet diapers per day after day 5, shows signs of jaundice worsening. These may indicate feeding difficulties, metabolic issues, or other conditions that need assessment.

Yes. Breastfed babies typically gain weight faster than formula-fed in the first 3 months, then slower from 3-12 months. By 12 months, the difference is minimal. WHO growth charts were developed from breastfed babies under optimal conditions, so breastfed babies may appear to 'underperform' on CDC charts in months 6-12: this is not a clinical problem.

Median weight at 12 months on the WHO charts: boys 9.6 kg (21.3 lb), girls 8.9 kg (19.7 lb). Many babies roughly triple their birth weight by 12 months. The 5th to 95th percentile range is 8.1 to 11.5 kg (17.8 to 25.4 lb) for boys and 7.3 to 11.0 kg (16.2 to 24.2 lb) for girls. Length at 12 months averages about 74-76 cm (29-30 inches). Head circumference: boys ~46 cm, girls ~45 cm.

In the US, CDC recommends the WHO growth charts from birth to 24 months and the CDC 2000 charts from age 2 to 19. The WHO charts are standards based on healthy breastfed babies raised in good conditions, so they show how babies should grow rather than just how they did grow. This calculator uses the same WHO data, so its percentile should match what you see at the clinic for the same weight and age.

Usually because of age or weighing differences. This calculator uses completed months, while clinic software uses the exact age in days, which can move a young baby by several percentile points. Weight with a diaper or clothes, a feed just before weighing, and different scales also matter. For a baby born early, the clinic may use corrected age. The trend across visits matters more than any single percentile.
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