Average Baby Weight by Month: Chart for Boys and Girls, Birth to 24 Months

The average baby weight is about 7.4 pounds (3.3 kg) for boys and 7.1 pounds (3.2 kg) for girls at birth, and about 21.3 pounds (9.6 kg) for boys and 19.7 pounds (8.9 kg) for girls at 12 months, according to the World Health Organization growth standards published by the CDC.

Those numbers are the 50th percentile, the exact middle of healthy babies. Half weigh more and half weigh less, so “average” is a midpoint, not a target your baby has to hit.

Below: the average baby weight by month in one chart, the healthy range around it, newborn weight loss, breastfed vs formula fed patterns, and what your pediatrician is really watching: the curve over time.

Average Baby Weight at a Glance

Every weight in this guide comes from the WHO Child Growth Standards weight-for-age data files that the Centers for Disease Control and Prevention (CDC) publishes. We downloaded the boys and girls files in October 2026 and converted kilograms to pounds at 1 kg = 2.2046 lb.

Why WHO data? The CDC states that the WHO Child Growth Standards “are recommended for plotting and tracking growth of US children from birth to 2 years.”

Average Baby Weight by Month: Birth to 24 Months

Each row is the midpoint for babies who have completed that many months. A baby is not behind for weighing less or ahead for weighing more. Shopping for clothes? Pair this chart with our baby clothes size chart.

Average Newborn Weight and the First Two Weeks

In the WHO data, the average newborn weight is 3.3 kg for boys (7.4 lb, about 7 lb 6 oz) and 3.2 kg for girls (7.1 lb, about 7 lb 2 oz). The 5th to 95th percentile range in the same files is 5.7 to 9.3 lb for boys and 5.6 to 8.9 lb for girls.

Then the number drops. The American Academy of Pediatrics (AAP) explains that birth weight includes excess body fluid that is lost in the first few days, and that all newborns lose weight during the first 7 days. Its timeline:

• First days: the AAP says a well-fed breastfed newborn should lose no more than 8 to 10 percent of birth weight before starting to gain again.
• From about day 5: babies should start gaining weight steadily.
• By about 2 weeks: they should be back at their original birth weight. Almost all babies have regained it by 3 weeks.
• First month: the average newborn gains almost an ounce (28 grams) a day, with growth spurts typically around 7 to 10 days and between 3 and 6 weeks.

The AAP advises a first checkup no more than 48 hours after hospital discharge. For feeding amounts, see how much a newborn should eat and our newborn feeding schedule.

What Percentiles Mean and the Healthy Range at Key Ages

A percentile ranks your baby’s weight against 100 babies of the same age and sex. At the 50th, half weigh more and half weigh less. At the 25th, about 25 of 100 weigh less and 75 weigh more.

A percentile is not a grade. The AAP puts it this way: “Unlike school grades that we hope are always as high as possible, for growth we hope for consistency.” It adds that when your child comes in at the 10th percentile, “it’s really no better or worse than coming in at the 90th.”

Falling outside that band does not by itself mean something is wrong. The outermost lines on the WHO charts are the 2.3rd and 97.7th percentiles (labeled 2nd and 98th), which the CDC says match the cutoff values the WHO recommends: 2 standard deviations from the median.

Average Weight for a 3, 6, 9 and 12 Month Old

• 3 months: 14.1 lb (6.4 kg) for boys and 12.9 lb (5.8 kg) for girls, about 6.7 lb and 5.8 lb above birth weight.
• 6 months: 17.5 lb (7.9 kg) for boys and 16.1 lb (7.3 kg) for girls, a gain of about 3.4 lb and 3.2 lb since 3 months.
• 9 months: 19.6 lb (8.9 kg) for boys and 18.1 lb (8.2 kg) for girls.
• 12 months: 21.3 lb (9.6 kg) for boys and 19.7 lb (8.9 kg) for girls, a gain of about 3.8 lb and 3.6 lb since 6 months.
• 24 months: 26.8 lb (12.2 kg) for boys and 25.3 lb (11.5 kg) for girls, about 5.5 lb (boys) and 5.6 lb (girls) more than at the first birthday.

The pattern is fast, then slower. Mayo Clinic describes it: in the first few months babies gain about 1 ounce (28 grams) a day, around 4 months that slows to about 20 grams a day, and as they turn 6 months many gain about 10 grams or less a day. Growth also comes in bursts, which we cover in baby growth spurts.

For skills at each age, see baby milestones by month.

When Do Babies Double and Triple Their Birth Weight?

You will hear rules of thumb about doubling and tripling birth weight. Mayo Clinic words the second one this way: looking at average growth, “most babies have tripled their birth weights by the first birthday.”

The WHO medians show how rough such rules are (our calculations from the CDC-published files):

• Double: the 50th percentile boy passes twice his birth weight (6.7 kg) between 3 and 4 months. The 50th percentile girl passes hers (6.5 kg) between 4 and 5 months.
• Triple: the 50th percentile boy reaches three times his birth weight (10.0 kg) between 13 and 14 months, and the 50th percentile girl (9.7 kg) between 15 and 16 months.

So the sources do not line up exactly: the WHO median baby triples a little after the first birthday. Treat both as rough guides, not tests, and ask at the next visit how your baby’s curve looks.

Breastfed vs Formula Fed Babies, and Why the Chart Changes at Age 2

Feeding method changes the shape of the curve. According to the CDC:

• Healthy breastfed infants typically put on weight more slowly than formula-fed infants in their first year.
• Formula-fed infants typically gain weight more quickly after about 3 months of age.
• The difference in weight patterns continues even after complementary foods are introduced.
• Growth in length is similar in both groups.

The WHO standards treat the breastfed baby as the norm: the CDC notes that all infants in the WHO sample were breastfed for at least 12 months and predominantly breastfed for at least 4 months, while the CDC’s own infant charts are based on primarily formula-fed infants. So a breastfed baby who gains a little more slowly after 3 months may simply be following the pattern the WHO charts were built on. Your pediatrician can confirm that from the curve. For amounts, see our formula feeding chart and how to breastfeed.

At age 2 (24 months), the CDC says providers should switch from the WHO charts to the CDC growth charts, which is why our table stops there. Expect a possible shift in percentile at that visit: the CDC notes children may be classified differently because measurement changes from lying-down length to standing height, and the comparison group changes from breastfed babies to a primarily formula-fed population.

Preemies, Corrected Age and Catch-Up Growth

If your baby was born early, the chart above will not fit without an adjustment. Nationwide Children’s Hospital explains that corrected age describes a child’s age from the original due date. A baby born 8 weeks early who is 16 weeks old has a corrected age of 8 weeks.

• Which chart: Nationwide Children’s describes the Fenton preterm growth chart as the main tool for premature babies, used together with term charts after 40 weeks.
• How long to correct: it recommends using corrected age through 2 years from the original due date, and notes that some experts correct through 3 years.
• Catch-up growth: rapid growth that narrows the size gap with term babies can occur during those 2 years. The rate varies with birth weight, gestational age at birth, genetic potential and medical condition.

Ask your pediatrician which chart and which age they are plotting.

What Affects Baby Weight and What Your Pediatrician Watches

The AAP lists genetics, environment, nutrition, activity and health problems as influences on how a child grows. Sex matters too: in the WHO data, the median boy is heavier than the median girl at every month from birth to 24 months.

Your pediatrician watches the line, not the dot. In the AAP’s words: “What we care about most is the trend at which your baby or child gains weight, height or head circumference.” It adds that one static point on the growth chart is not as useful as evaluating 5 data points over time. For children under 2, weight is read alongside length and head circumference.

• Keep every well visit, since each one adds a point to the curve, and ask to see the chart.
• Tell the pediatrician about feeding changes, illness or a drop in appetite. See baby not eating as much and starting solids.
• If you like to log weights between visits, our roundup of the best baby growth tracking apps can help.

Related Betteroo Guides

• Baby growth spurts
• How much should a newborn eat?
• Baby feeding chart
• Baby milestones by month
• Baby clothes size chart
• Best baby growth tracking apps

When to Call Your Pediatrician

Do not wait for the next well visit if you are worried. Call your pediatrician if:

• Your newborn is not back to birth weight by about 2 weeks: the AAP says babies should be by then, and almost all are by 3 weeks.
• Your newborn has lost a lot of weight: the AAP says a well-fed breastfed newborn loses no more than 8 to 10 percent of birth weight in the first few days.
• There are too few wet or dirty diapers: by 5 to 7 days old, the AAP says a breastfed baby should have 6 or more wet diapers a day and at least 3 to 4 yellow, loose stools.
• A newborn is feeding too little: the AAP says breastfed newborns should nurse at least 8 to 12 times every 24 hours.
• The curve changes: weight flattens, drops, or tracks well below where it had been across several weigh-ins. The trend is what the AAP says pediatricians care about most.

If your baby seems seriously unwell and you cannot reach your pediatrician right away, go to the nearest emergency room or call 911. This article is general education, not medical advice. Only your child’s own clinician can judge your child’s growth.

Frequently Asked Questions