Your baby
We use the corrected age (from the due date) until age 2, as pediatricians do.
The due date gives the exact correction; the weeks are fine if you don't have it. What is corrected age?
Measurements
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Results
Your baby's curve will appear here.
- Anywhere from the 3rd to the 97th percentile is the usual range. The 50th is the average, not the goal: a baby on the 10th percentile can be every bit as healthy as one on the 90th.
- The curve matters more than the number. A baby who follows roughly the same line over time is growing well, wherever that line is.
- Crossing two or more of the main lines, especially downward, is worth a chat with your pediatrician.
- These are the WHO charts US pediatricians use from birth to age 2, built from healthy breastfed babies in six countries.
How to read your baby's percentile
A percentile compares your baby with 100 healthy babies of the same age and sex. The 40th percentile for weight means your baby is heavier than 40 of them and lighter than the other 60. It is not a grade. Nobody is aiming for 100, and 50 is simply the middle of the crowd.
Small parents tend to have small babies, and tall parents long ones, so a baby who sits on the 15th percentile month after month is usually just built that way. That is why one measurement is a snapshot and three are a story: what your pediatrician watches is the line the dots make, which is exactly what the chart above draws for you.
Weight-for-length is the fourth number, and often the most reassuring one. It ignores age and asks a simpler question: does the weight fit the length? A long, lean baby can be on the 20th percentile for weight and still sit right in the middle for weight-for-length.
When a change in percentile matters
- Moving one band in the first year is common. Many babies drift up or down a line as they leave behind the size of the womb and settle onto the curve their genes have in mind (catch-up and catch-down growth). It usually happens by 6 to 18 months, then the line steadies.
- Crossing two or more major lines (say from above the 85th to below the 15th) is the classic sign your pediatrician will want to look into, especially if it is weight going down.
- Below the 3rd or above the 97th isn't a diagnosis. About 3 in 100 healthy babies live there. It simply means the doctor will look at the whole picture: parents' sizes, feeding, development, how the curve has moved.
- Head growth that suddenly speeds up or stalls deserves a mention at the next checkup, even if the percentile itself looks fine.
If your baby seems unwell, isn't feeding, or has far fewer wet diapers, call your pediatrician, whatever the chart says.
How much weight should a baby gain per week?
Babies first lose a little: up to 7% of their birth weight in the first days is normal, and most are back to birth weight by 10 to 14 days. After that, the typical (median) weekly gain on the WHO standards is:
| Age | Girls, per week | Boys, per week |
|---|---|---|
| 0–3 months | about 7 oz (200 g) | about 8 oz (230 g) |
| 3–6 months | about 4 oz (110 g) | about 4 oz (120 g) |
| 6–12 months | about 2¼ oz (65 g) | about 2¼ oz (65 g) |
| 1–2 years | about 1¾ oz (50 g) | about 1¾ oz (50 g) |
In other words, a typical baby doubles their birth weight at about 3½ months (boys) to 4 months (girls) and weighs about 2.8 to 2.9 times their birth weight at one year, a little under the old "triples by one" rule. Week-to-week numbers bounce around with feeds, diapers and the scale, so look at the gain over a month. Add two measurements in the calculator and it shows your baby's own weekly gain next to the typical one for that age.
Why we use the WHO charts
The WHO Child Growth Standards (2006) were built from about 8,500 healthy children in Brazil, Ghana, India, Norway, Oman and the USA, raised in good conditions and breastfed as babies. They show how children should grow, not just how a particular group happened to grow, which is why the CDC and the American Academy of Pediatrics recommend them for every child under 2.
From age 2, US pediatricians switch to the CDC charts, so for toddlers between 2 and 5 your doctor's number can differ from this one by a few percentiles. Both are fine; what matters is that the curve keeps its shape on whichever chart you follow. Formula-fed babies often track a little higher after 3 to 4 months, and that is fine too.
Measuring at home without fooling yourself
- Measure the same way every time. Same scale, same time of day, ideally before a feed and in a dry diaper or nothing at all.
- Hold-and-subtract works, roughly. Weigh yourself, then yourself holding the baby, and subtract. Bathroom scales are often off by 100 to 200 g (4 to 7 oz), so watch the trend over weeks, not single readings.
- Length needs two people. Baby flat on their back, one person holds the head against a book or wall, the other straightens the knees and marks the heel. Even at the doctor's office length is often 1 to 2 cm (½ to ¾ in) off, so one odd reading means little.
- Head: tape above the eyebrows and ears. Run a soft tape around the widest part of the back of the head, measure three times and keep the largest.
- Use the checkup numbers when you have them. Your pediatrician's scale and length board are better than anything at home; type those in and the curve will be at its most honest.
Average baby weight, length and head size by month (WHO)
This is the average baby weight by month, plus length (height from 2 years) and head circumference, from the WHO baby growth chart for girls and boys. The bold number is the median (50th percentile); underneath is the usual range, the 3rd to the 97th percentile. So, how much should a 6 month old weigh? Girls about 7.3 kg (16 lb 2 oz) and boys about 7.9 kg (17 lb 8 oz), and the usual range runs from about 13 to 20 lb for girls and 14 to 21½ lb for boys. Tap an age for its full table, from the 3rd to the 97th percentile.
Girls
| Age | Weight | Length / height | Head |
|---|---|---|---|
| Birth | 7 lb 2 oz (3.2 kg) 5 lb 6 oz – 9 lb 3 oz | 19¼ in (49.1 cm) 18 – 20¾ in | 13¼ in (33.9 cm) 12½ – 14¼ in |
| 1 month | 9 lb 3 oz (4.2 kg) 7 lb 1 oz – 11 lb 13 oz | 21 in (53.6 cm) 19¾ – 22½ in | 14½ in (36.5 cm) 13½ – 15¼ in |
| 2 months | 11 lb 5 oz (5.1 kg) 8 lb 13 oz – 14 lb 6 oz | 22½ in (57.1 cm) 21 – 24 in | 15 in (38.3 cm) 14¼ – 16 in |
| 3 months | 12 lb 14 oz (5.8 kg) 10 lb 2 oz – 16 lb 5 oz | 23½ in (59.8 cm) 22 – 25 in | 15½ in (39.5 cm) 14¾ – 16½ in |
| 4 months | 14 lb 3 oz (6.4 kg) 11 lb 4 oz – 17 lb 14 oz | 24½ in (62.1 cm) 22¾ – 26 in | 16 in (40.6 cm) 15 – 17 in |
| 5 months | 15 lb 3 oz (6.9 kg) 12 lb 1 oz – 19 lb 3 oz | 25¼ in (64.0 cm) 23½ – 26¾ in | 16¼ in (41.5 cm) 15¼ – 17¼ in |
| 6 months | 16 lb 2 oz (7.3 kg) 12 lb 13 oz – 20 lb 5 oz | 26 in (65.8 cm) 24¼ – 27½ in | 16½ in (42.2 cm) 15¾ – 17½ in |
| 7 months | 16 lb 14 oz (7.6 kg) 13 lb 7 oz – 21 lb 4 oz | 26½ in (67.3 cm) 24¾ – 28¼ in | 16¾ in (42.8 cm) 16 – 17¾ in |
| 8 months | 17 lb 9 oz (8.0 kg) 14 lb – 22 lb 2 oz | 27 in (68.8 cm) 25¼ – 28¾ in | 17 in (43.4 cm) 16 – 18 in |
| 9 months | 18 lb 2 oz (8.2 kg) 14 lb 8 oz – 22 lb 14 oz | 27½ in (70.1 cm) 25¾ – 29½ in | 17¼ in (43.8 cm) 16¼ – 18¼ in |
| 10 months | 18 lb 11 oz (8.5 kg) 14 lb 15 oz – 23 lb 10 oz | 28¼ in (71.5 cm) 26¼ – 30 in | 17½ in (44.2 cm) 16½ – 18½ in |
| 11 months | 19 lb 4 oz (8.7 kg) 15 lb 6 oz – 24 lb 5 oz | 28¾ in (72.8 cm) 26¾ – 30½ in | 17½ in (44.6 cm) 16½ – 18½ in |
| 12 months | 19 lb 12 oz (8.9 kg) 15 lb 12 oz – 25 lb | 29¼ in (74.0 cm) 27¼ – 31 in | 17¾ in (44.9 cm) 16¾ – 18¾ in |
| 15 months | 21 lb 3 oz (9.6 kg) 16 lb 14 oz – 26 lb 14 oz | 30½ in (77.5 cm) 28½ – 32½ in | 18 in (45.7 cm) 17 – 19 in |
| 18 months | 22 lb 9 oz (10.2 kg) 18 lb – 28 lb 10 oz | 31¾ in (80.7 cm) 29¾ – 34 in | 18¼ in (46.2 cm) 17¼ – 19¼ in |
| 2 years (24 mo) | 25 lb 5 oz (11.5 kg) 20 lb 3 oz – 32 lb 3 oz | 34 in (86.4 cm) 31¾ – 36½ in | 18½ in (47.2 cm) 17½ – 19½ in |
| 3 years (36 mo) | 30 lb 9 oz (13.9 kg) 24 lb 3 oz – 39 lb 5 oz | 37½ in (95.1 cm) 34½ – 40¼ in | 19 in (48.5 cm) 18 – 20¼ in |
| 4 years (48 mo) | 35 lb 7 oz (16.1 kg) 27 lb 9 oz – 46 lb 9 oz | 40½ in (102.7 cm) 37¼ – 43¾ in | 19½ in (49.3 cm) 18¼ – 20½ in |
| 5 years (60 mo) | 40 lb 3 oz (18.2 kg) 30 lb 13 oz – 53 lb 14 oz | 43 in (109.4 cm) 39½ – 46½ in | 19¾ in (49.9 cm) 18½ – 20¾ in |
Boys
| Age | Weight | Length / height | Head |
|---|---|---|---|
| Birth | 7 lb 6 oz (3.3 kg) 5 lb 8 oz – 9 lb 9 oz | 19¾ in (49.9 cm) 18¼ – 21 in | 13½ in (34.5 cm) 12¾ – 14½ in |
| 1 month | 9 lb 13 oz (4.5 kg) 7 lb 9 oz – 12 lb 9 oz | 21½ in (54.7 cm) 20 – 23 in | 14¾ in (37.2 cm) 13¾ – 15½ in |
| 2 months | 12 lb 5 oz (5.6 kg) 9 lb 11 oz – 15 lb 7 oz | 23 in (58.4 cm) 21½ – 24½ in | 15½ in (39.1 cm) 14½ – 16¼ in |
| 3 months | 14 lb 1 oz (6.4 kg) 11 lb 3 oz – 17 lb 7 oz | 24¼ in (61.4 cm) 22¾ – 25¾ in | 16 in (40.5 cm) 15 – 16¾ in |
| 4 months | 15 lb 7 oz (7.0 kg) 12 lb 7 oz – 19 lb 1 oz | 25¼ in (63.9 cm) 23½ – 26¾ in | 16½ in (41.6 cm) 15½ – 17¼ in |
| 5 months | 16 lb 9 oz (7.5 kg) 13 lb 6 oz – 20 lb 5 oz | 26 in (65.9 cm) 24½ – 27½ in | 16¾ in (42.6 cm) 15¾ – 17¾ in |
| 6 months | 17 lb 8 oz (7.9 kg) 14 lb 3 oz – 21 lb 7 oz | 26¾ in (67.6 cm) 25 – 28¼ in | 17 in (43.3 cm) 16¼ – 18 in |
| 7 months | 18 lb 5 oz (8.3 kg) 14 lb 14 oz – 22 lb 6 oz | 27¼ in (69.2 cm) 25½ – 28¾ in | 17¼ in (44.0 cm) 16½ – 18¼ in |
| 8 months | 19 lb (8.6 kg) 15 lb 7 oz – 23 lb 4 oz | 27¾ in (70.6 cm) 26¼ – 29½ in | 17½ in (44.5 cm) 16½ – 18½ in |
| 9 months | 19 lb 10 oz (8.9 kg) 15 lb 15 oz – 24 lb 1 oz | 28¼ in (72.0 cm) 26¾ – 30 in | 17¾ in (45.0 cm) 16¾ – 18¾ in |
| 10 months | 20 lb 3 oz (9.2 kg) 16 lb 7 oz – 24 lb 12 oz | 28¾ in (73.3 cm) 27¼ – 30½ in | 17¾ in (45.4 cm) 17 – 18¾ in |
| 11 months | 20 lb 12 oz (9.4 kg) 16 lb 14 oz – 25 lb 7 oz | 29¼ in (74.5 cm) 27½ – 31 in | 18 in (45.8 cm) 17 – 19 in |
| 12 months | 21 lb 4 oz (9.6 kg) 17 lb 5 oz – 26 lb 1 oz | 29¾ in (75.7 cm) 28 – 31½ in | 18¼ in (46.1 cm) 17¼ – 19 in |
| 15 months | 22 lb 12 oz (10.3 kg) 18 lb 8 oz – 27 lb 15 oz | 31¼ in (79.2 cm) 29¼ – 33 in | 18½ in (46.8 cm) 17½ – 19½ in |
| 18 months | 24 lb 2 oz (10.9 kg) 19 lb 9 oz – 29 lb 11 oz | 32½ in (82.3 cm) 30½ – 34½ in | 18¾ in (47.4 cm) 17¾ – 19¾ in |
| 2 years (24 mo) | 26 lb 13 oz (12.1 kg) 21 lb 10 oz – 33 lb 3 oz | 34½ in (87.8 cm) 32¼ – 36¾ in | 19 in (48.2 cm) 18 – 20 in |
| 3 years (36 mo) | 31 lb 10 oz (14.3 kg) 25 lb 4 oz – 39 lb 13 oz | 37¾ in (96.1 cm) 35 – 40½ in | 19½ in (49.5 cm) 18½ – 20½ in |
| 4 years (48 mo) | 36 lb 1 oz (16.3 kg) 28 lb 7 oz – 46 lb | 40¾ in (103.3 cm) 37½ – 43¾ in | 19¾ in (50.2 cm) 18¾ – 20¾ in |
| 5 years (60 mo) | 40 lb 7 oz (18.3 kg) 31 lb 8 oz – 52 lb 6 oz | 43¼ in (110.0 cm) 39¾ – 46¾ in | 20 in (50.7 cm) 18¾ – 21 in |
Length is measured lying down until 2 years and height standing up after that. A child measured standing is about 0.7 cm (¼ in) shorter than lying down, which is why the WHO curves take a small step down at 24 months. Ages in days follow the WHO convention (one month = 30.4375 days).
Questions
What percentile should my baby be in?
Anywhere between the 3rd and the 97th percentile is the usual range, and no spot in it is better than another. The 50th is the average, not a target. What your pediatrician cares about is that your baby keeps following roughly the same curve over time, at whatever height on the chart it runs.
Is the 5th (or 10th) percentile bad?
No. Five or ten in every hundred healthy babies are there, often because their parents are on the small side. If your baby has stayed around that line, is feeding well and has plenty of wet diapers, a low percentile is just a small baby growing nicely. It's worth a closer look only if the curve has been falling, or if it's below the 3rd.
My baby dropped from the 75th to the 25th percentile. Should I worry?
It deserves a conversation, not panic. In the first year many babies drift a band as they settle onto their genetic curve, and a single home measurement can easily be off. A move from the 75th to the 25th is about two bands, the size of change pediatricians like to look into, so mention it at the next visit, sooner if your baby is feeding poorly, has fewer wet diapers or seems unwell. Check the trend card above: it tells you how many bands the curve has actually moved.
WHO vs CDC growth charts: which one is right?
Both, for different ages. The CDC and the American Academy of Pediatrics recommend the WHO charts from birth to 2, because they show how healthy breastfed babies grow, and the CDC charts from 2 onward. Between 2 and 5 the two can differ by a few percentiles; the shape of your child's curve matters more than which chart drew it.
Do breastfed and formula-fed babies grow differently?
A little. They grow about the same for the first few months; after 3 to 4 months formula-fed babies tend to gain weight a bit faster. The WHO standards are based on breastfed babies, so a formula-fed baby running slightly above their earlier line later in the first year is normal and nothing to fix.
How much weight should my baby gain per week?
After getting back to birth weight by about two weeks, a typical baby gains about 7 to 8 oz (200 to 230 g) a week in the first three months, about 4 oz (110 to 120 g) from 3 to 6 months, and about 2¼ oz (65 g) from 6 to 12 months. Add two measurements above and the calculator shows your baby's own weekly gain next to the typical one for that age.
How does corrected age work for a premature baby?
Corrected age counts from the due date instead of the birth date. A baby born at 32 weeks is 8 weeks early, so at 5 months old they are compared with 3-month-old babies. Pediatricians use corrected age until about 2 years, after which most preemies have caught up. Pick "Born early?" in the calculator and add the due date or the weeks, and it does this for you. The corrected age calculator shows the corrected age on its own.
What does weight-for-length mean?
It compares your baby's weight with babies of the same length, whatever their age. It answers "is the weight right for the size?", which is why pediatricians use it to spot a baby who is too thin or getting heavy for their frame. From age 2 it becomes weight-for-height, measured standing.
What is a z-score?
It's the percentile's more precise twin: how many standard deviations your baby is from the median. 0 is the 50th percentile, −1 is about the 16th, +1 about the 84th, and ±2 are roughly the 2nd and 98th. Doctors use z-scores because they keep working at the extremes, where percentiles bunch up. Open "Details" on any result card to see it.
Is what I type private?
Yes. It's calculated on your phone, saved only on your phone, and the share link keeps the numbers after the #, which browsers never send to a server, the same way Mamoon keeps your nursery video on your own Wi-Fi. Your baby's name never goes into the link.
Sources
- World Health Organization, WHO Child Growth Standards and the expanded tables for weight, length/height, head circumference and weight-for-length/height.
- WHO, anthro R package: the LMS tables (growthstandards data) this calculator uses, and the restricted z-score method for weight.
- WHO Multicentre Growth Reference Study Group, WHO Child Growth Standards: Methods and development (2006), chapter 7 on computing percentiles and z-scores.
- CDC, Recommended growth charts (why WHO charts are recommended under 2 and CDC charts from 2).
- American Academy of Pediatrics, Bright Futures periodicity schedule (the checkup ages used for the projection).
Spotted a mistake or an outdated figure? Write to [email protected].