How much weight should a baby gain in the first year?
Typical baby weight gain month by month in the first year, with WHO median weights for boys and girls from birth to 12 months.
Educational content only, not medical advice. Always talk to your doctor or health visitor about your child.
In this article
Most babies gain weight fastest in the first three months, then the pace gradually slows through the rest of the first year. Using the WHO Child Growth Standards, the median baby boy goes from about 3.3 kg at birth to about 9.6 kg at 12 months, and the median baby girl from about 3.2 kg to about 9.0 kg. Your own baby may be lighter or heavier than the median and still be growing perfectly well. The steady curve over time is what matters most.
Below you will find the WHO median weights at key ages, what happens in the first two weeks, and what usually affects the pace of weight gain.
What is a normal weight for a baby each month?
These figures are the WHO 50th percentile (median) weights, rounded to one decimal place. Half of healthy babies weigh less than this at each age and half weigh more. They are a middle point, not a target.
Boys (WHO median)
- Birth: 3.3 kg
- 1 month: 4.5 kg
- 2 months: 5.6 kg
- 3 months: 6.4 kg
- 4 months: 7.0 kg
- 6 months: 7.9 kg
- 9 months: 8.9 kg
- 12 months: 9.6 kg
Girls (WHO median)
- Birth: 3.2 kg
- 1 month: 4.2 kg
- 2 months: 5.1 kg
- 3 months: 5.8 kg
- 4 months: 6.4 kg
- 6 months: 7.3 kg
- 9 months: 8.2 kg
- 12 months: 9.0 kg
If you look at the gaps between these numbers, you can see the pattern clearly. Between birth and 3 months the median boy gains roughly 3 kg, while between 6 and 12 months he gains under 2 kg. The same slowing happens for girls. A baby who is gaining less per month at 8 months than at 8 weeks is usually doing exactly what babies do.
To see where your own baby sits, you can enter their clinic measurements into our free baby growth calculator, which compares them with the WHO data for their age and sex.
Is it normal for a newborn to lose weight?
Yes. It is very common for babies to lose some weight in the first few days after birth. They are passing their first stools, losing extra fluid, and feeding is still getting established. Most babies are back to their birth weight within about 2 weeks.
Your midwife or health visitor will usually weigh your baby during this time. If your baby has lost more than expected, or is slow to get back to birth weight, they will look at feeding with you and decide whether any extra support is needed. This is a routine part of newborn care, and it is one of the reasons those early weigh-ins happen.
How much weight does a baby gain per week?
People often look for a weekly number, but weight gain is lumpy. A baby might gain a lot one week and very little the next, especially around growth spurts, illness or changes in feeding. Looking at the WHO medians, the fastest gains happen in the first couple of months, and gains get noticeably smaller in the second half of the year.
A few things that are worth knowing:
- Weekly weighing can mislead. Different scales, a full nappy or a recent feed can easily change the reading by more than a week of real growth.
- Monthly trends are clearer. Plotting a measurement every few weeks on a growth chart shows the real pattern.
- Your health professional knows the context. They look at feeding, nappies, alertness and development as well as the scales.
What affects how fast my baby gains weight?
Lots of ordinary things change the pace of weight gain:
- Birth weight and genetics. Smaller parents often have smaller babies, and babies born large may drift down towards their own line.
- Prematurity. Preterm babies are usually plotted by corrected age, and their pattern can look different from babies born at term.
- Feeding. Breastfed and formula-fed babies can follow slightly different patterns, particularly after the first few months. The WHO standards were built mainly from breastfed babies.
- Illness. A tummy bug or a bad cold can cause a short pause in weight gain, usually followed by a catch-up.
- Starting solids. From around 6 months, as babies start eating food, weight gain often stays steady rather than speeding up. Milk is still the main source of nutrition at first. See our starting solids guide for more.
- Moving more. Babies who start rolling, crawling and cruising burn more energy, which can make the curve flatten slightly.
When should I talk to a doctor about my baby's weight?
This article is educational and not medical advice. Your doctor, health visitor or paediatrician is the right person to talk to about your own baby. It is worth getting in touch if you notice things like:
- Fewer wet nappies than usual, or very dark urine
- Your baby seems unusually sleepy, floppy or hard to wake for feeds
- Feeding has become difficult or very short
- Measurements show a steady drop across percentile lines over time
- You simply have a feeling something is not right
Trust your instincts. Health professionals would much rather see a baby who turns out to be fine than miss one who needs help.
How do I keep track of my baby's weight?
The most useful thing you can do is keep every measurement in one place, with the date. That way, when you sit down with your health visitor, you can look at the curve together rather than trying to remember numbers. If you want to understand the chart itself, our guide to baby growth percentiles explains what the lines mean and why the 15th percentile is perfectly normal.
Baby Growth Tracker Pro is built for exactly this. You add each weight and it is plotted on WHO growth charts with percentiles from birth to 5 years, with corrected age for preterm babies. It also has a daily care log for feeds, nappies, sleep and temperature that you can fill in with one tap, which can be handy to show at appointments. It works offline and does not need an account. Find out more on the Baby Growth Tracker page.
A rough rule of thumb
You may hear that babies roughly double their birth weight by around 4 to 5 months and roughly triple it by their first birthday. The WHO medians above fit that pattern loosely, but plenty of healthy babies do it a little sooner or later. Use it as a general idea, not a test your baby has to pass.
Frequently asked questions
How much weight should a baby gain in the first month?
Using the WHO medians, the typical baby gains around 1 kg between birth and 1 month, and that includes getting back to birth weight after the first few days. Individual babies vary a lot.
Why has my baby's weight gain slowed down?
Weight gain naturally slows after the first few months. By the second half of the first year, a smaller monthly gain is expected, especially once your baby is moving more.
Are the WHO medians the weight my baby should be?
No. The median is the middle of a healthy range. Your baby can be well below or above it and be growing well, as long as they follow a steady curve and your health professional is happy.
Should I weigh my baby at home every week?
Usually there is no need. Home scales are less accurate, and frequent weighing can cause unnecessary worry. Follow the schedule your clinic or health visitor suggests.
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