Growth charts are one of the most-looked-at but least-explained tools in your baby's red book. Here's how to actually read them.
The UK growth charts (from the WHO/UK Growth Reference) show centile lines — 0.4th, 2nd, 9th, 25th, 50th, 75th, 91st, 98th, and 99.6th.
A centile tells you what proportion of babies are smaller than your baby at that age. If your baby is on the 50th centile for weight, they weigh more than 50% of babies their age — and less than the other 50%. Right in the middle.
If your baby is on the 9th centile, they weigh more than 9% of babies their age — in the lower-smaller range, but entirely normal.
There is no "right" centile. A baby consistently on the 9th centile is growing as normally as one consistently on the 75th.
Weight: Measured in kilograms. Most commonly plotted.
Length/height: Measured lying down (length) until 2 years, then standing (height). Requires two people to measure accurately.
Head circumference: Measured with a tape around the widest point of the head. Tracks brain growth.
All three should be plotted and compared — a baby small in all three is likely constitutionally small; a baby whose head is far above weight and height may warrant investigation.
A single measurement tells you relatively little. What matters is the pattern over time.
Healthy growth looks like: Measurements staying roughly within the same centile band (within one to two centile spaces) over time, with a smooth upward curve.
Worth discussing with your health visitor or GP:
| Age | Average weight | |-----|----------------| | Birth | 3.3 kg (7.3 lbs) | | 1 month | 4.2 kg | | 2 months | 5.1 kg | | 3 months | 5.8 kg | | 4 months | 6.4 kg | | 6 months | 7.6 kg | | 9 months | 8.9 kg | | 12 months | 9.8 kg |
These are averages — healthy babies range widely above and below these figures.
It's normal for babies to shift centile in the first few months. Birth weight is affected by maternal size, placental function, and gestational factors. After birth, babies often shift towards their genetic centile — the growth trajectory determined by their parents' heights and builds. This shift typically stabilises by 6–12 weeks.
WHO Growth Standards: Used for all children in the UK. Based on children raised in optimal health conditions globally, used from birth to 4 years.
Premature babies: Plots must be adjusted for corrected age (subtract weeks premature from chronological age). A baby born 8 weeks early who is 16 weeks old should be plotted at 8 weeks corrected age. This adjustment is usually made until 2 years of age.
Breastfed vs formula-fed: The UK now uses WHO charts which are based on breastfed babies. Formula-fed babies may plot slightly higher on weight — this is normal and not a concern.
NHS guidance:
Frequent weighing of a healthy, well-feeding, thriving baby increases parental anxiety without clinical value and can undermine confidence in breastfeeding. If baby looks well, is alert, has good wet nappies, and is meeting developmental milestones — they're almost certainly fine.
Growth charts track physical growth. They don't capture:
A thriving baby who is alert, engaged, feeding well, and developing appropriately is healthy — even if they plot below average on a chart. Always consider the whole picture.
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