Baby weight gain by age: what is normal

Weight is the number parents check most and understand least. It is also the one most likely to be looked up in a panic at midnight, so here is the shape of normal — with the loud caveat that a single measurement carries almost no information on its own.

The first two weeks look wrong and are not

Nearly all newborns lose weight in the first days. Up to about 10% of birth weight is considered within normal, and it is mostly fluid rather than anything to do with how feeding is going.

The expectation is that birth weight is regained by around two weeks. This is one of the specific things a midwife or health visitor is watching in the early visits, and it is the single most useful early checkpoint there is.

Typical weekly gain by age

These are averages across large populations. A baby at the bottom of every row can be perfectly healthy, provided they are consistently at the bottom of every row — which is what “following their own curve” means in practice, and what the WHO growth percentiles are for.

The daily column is there because it is what gets searched for, not because it is worth measuring. Twenty to thirty grams is well inside the margin of a full nappy, a recent feed or a different vest, so a daily figure is arithmetic rather than an observation. Weekly is the shortest interval at which the number means anything, and monthly is better.

Why the numbers slow down so much

The drop from 200g a week to 40g a week is startling written down, and it is exactly what should happen. A newborn is doing the fastest growing of their life; a toddler is spending their energy on moving, learning and talking instead.

This is also why toddler appetite becomes so erratic. A one-year-old needs proportionally far less food than a six-month-old, and the drop in interest that alarms parents at around a year is usually just growth slowing down on schedule.

How often to weigh

Less than you think. The usual pattern is frequent weighing in the first weeks, then monthly, then every few months.

• Weekly weighing mostly measures noise. A full nappy, a recent feed and different clothing can swing the reading more than a week of growth.
• Use the same scale. Home scales and clinic scales rarely agree; comparing across them invents trends that do not exist.
• Weigh under similar conditions. Same time of day, before a feed, same amount of clothing or none.

If a professional has asked you to weigh more often, follow that. Otherwise frequent weighing reliably produces anxiety and rarely produces information.

Breastfed and formula-fed babies gain differently

Breastfed babies typically gain faster in the first two to three months and more slowly after that. Formula-fed babies often show the reverse.

This is the whole reason the WHO charts exist and are used from birth to two. They are built from breastfed infants growing in good conditions, so they describe how growth should look rather than how a mixed population happened to grow. Plotting a breastfed baby against a formula-based reference can make entirely normal growth appear to falter around four months.

What a healthy pattern looks like

Not a number — a shape. Clinicians are looking for:

• A line roughly parallel to the printed curves, wherever it sits
• Weight, length and head circumference broadly in proportion
• Steady progress rather than a smooth one, since real data is bumpy
• A baby who is alert, feeding, and producing plenty of wet nappies

That last one deserves more weight than it usually gets. Six or more heavy wet nappies a day after the first week is a better everyday indicator of adequate intake than any scale.

Patterns worth raising

None of these means something is wrong. They mean a professional should look, which is a different and much less frightening thing.

What to do with the numbers

Very little, most of the time. The genuinely useful habits are small:

• Record each measurement with its date and plot it, rather than remembering the last one
• Look at the shape across months, not the gap between two readings
• Take the whole record to appointments — a trend answers questions a single figure cannot
• Resist comparing with other babies; they are on their own curves

When to ask

Speak to your paediatrician, midwife or health visitor if birth weight is not regained by two to three weeks, if weight crosses two major lines or plateaus, if wet nappies drop off, if your baby is very difficult to wake for feeds, or if feeding is consistently distressing. Early feeding problems are common and usually straightforward to fix — and much easier the sooner someone looks.