How much should a baby weigh? Month by month, honestly

Typical gains, with the caveat first

These are averages, and half of all healthy babies are below any average. Use them as a rough orientation and the growth chart as the actual guide.

The usual pattern: a loss of up to 7-10% of birth weight in the first days, regained by about two weeks. Then roughly 150-200 g a week for the first three months, around 100-150 g a week from three to six months, and 70-100 g a week from six to twelve months.

As landmarks: most babies double their birth weight by around four to six months and triple it by around a year. A baby born at 3 kg is therefore often around 6 kg at five months and around 9 kg at a year — with a wide legitimate range around all of those.

Breastfed and formula-fed babies grow at slightly different rates after the first months; the WHO charts are built on breastfed growth, which is the standard.

Why the number in your head is probably wrong

Birth weight sets the starting line. A baby born at 2.6 kg and a baby born at 3.6 kg are not supposed to weigh the same at six months.

Prematurity shifts everything: use corrected age for the first two years, so a baby born two months early is measured against the chart for their corrected age.

Illness causes dips and recovery causes catch-up. A week of diarrhoea or a bad cold shows on the chart and usually corrects itself.

And genetics decides a great deal. Small parents have smaller babies, and no amount of feeding changes a healthy child's frame.

When weight is genuinely a problem

The signals that matter: no weight gain over several weeks, weight crossing downward through two major percentile lines, weight below the 3rd percentile, or weight falling while length keeps rising.

Common correctable causes: feeding problems (poor latch, too-fast teat, insufficient volume), anaemia, worms, repeated infections, undiagnosed cow's-milk protein allergy, too much milk crowding out solids after a year, and — very commonly in India — too little iron and protein in the toddler diet.

Overweight matters too, and is rising: a baby whose weight is climbing much faster than length, particularly on bottle feeds or with early sugary snacks, deserves the same attention as an underweight one.

For under-fives, the Anganwadi and the health system monitor growth free, and supplementary nutrition is available for children identified as underweight. Use it — it is one of the better-run parts of Indian public health.

When to see a doctor

Same-day: a baby losing weight, refusing feeds, fewer than six wet nappies a day after the first week, lethargic or hard to wake, or with signs of dehydration.

Book an appointment for: no gain over three to four weeks in the first year, crossing two percentile lines downward, a baby who tires quickly during feeds, persistent vomiting or diarrhoea, or a family worry that the baby looks thin — a check and a haemoglobin test settle it either way.

This article is general information, not medical advice, and is no substitute for personal medical advice. For any decision about your or your child's health, please consult your doctor.

Frequently asked questions

Q: Everyone says my baby is thin. — Ask for the chart rather than opinions. A baby tracking steadily on their own curve, feeding well and passing plenty of urine is thriving whatever the relatives say.

Q: Can I give a supplement or tonic to make him gain? — Not without a cause being found. Most tonics are vitamins with marketing; some contain steroids or appetite stimulants that are not appropriate for children. Get haemoglobin, feeding and worms checked first.

Q: My baby gained very little this month. — One flat month, particularly during teething or illness, is common. Two or three in a row is a reason to be seen.

Q: Does formula make babies gain more than breastmilk? — Formula-fed babies do tend to gain faster in the second half of the first year, which is why the WHO charts are built on breastfed growth. Faster is not better.