Calculate height-for-age centile
Why height-for-age is the chronic growth indicator
Weight can change in weeks. Height cannot. A child's length or height is the cumulative record of months and years of nutrition, health and care, which makes height-for-age the indicator for stunting: the long-term failure to reach linear growth potential. Stunting is associated with impaired cognitive development, reduced school attainment and lower adult earnings, and unlike wasting it is largely irreversible after the first two years, which is why the global nutrition community treats the first 1,000 days as the critical window.
Because height changes slowly, a single measurement mostly describes the past, while the trend describes the present. A child whose height centile is steady, even if low, is growing at a normal velocity along their own curve. A child whose centile is falling is not, and that is the finding that should prompt investigation even when the absolute centile still looks acceptable.
Height-for-age also separates the two faces of undernutrition. A stunted child may have a normal weight-for-length, because their weight is appropriate for their short stature; weight-for-age alone would call them underweight and miss the real story. Plotting both indicators is what distinguishes a child who is proportionally small from one who is acutely thin.
Measuring correctly: the 0.7 cm rule
Technique matters more for length than for almost any other measurement. Children under 24 months must be measured lying down on a length board, with the head held against the fixed headboard, legs straightened and the movable footboard pressed firmly against the heels. From 24 months, children are measured standing with a stadiometer: heels, buttocks and shoulder blades against the board, head in the Frankfurt plane, gentle upward pressure under the jaw.
Standing height reads about 0.7 cm less than recumbent length in the same child, because the spine compresses slightly under gravity. The WHO reference reflects this: its tables are built on length below 24 months and height from 24 months. If you measure a 20-month-old standing, add 0.7 cm before comparing; if you measure a 30-month-old lying down, subtract 0.7 cm. This calculator applies the correction automatically when you tell it how the child was measured. A missing correction is one of the commonest causes of an apparent centile fall at the second birthday, when clinics switch from board to stadiometer.
Reading the result
The WHO defines stunting as height-for-age below -2 z-scores (about the 2.3rd centile) and severe stunting below -3. Between -2 and +2 is the normal range. Above +2 is tall for age, which is usually simply familial and only prompts endocrine thought when the growth pattern itself is abnormal, for example a very tall child with an accelerating velocity.
Always adjust the interpretation for parents' heights. A child of two short parents tracking steadily on the 5th centile is most likely expressing their genetic potential, while the same centile in a child of tall parents, or a centile that is falling, deserves investigation. The mid-parental height gives the expected adult target; in childhood, the question is whether the child is growing along a sensible curve toward it.
Worked examples
Example 1. A 12-month-old boy measured lying down at 75.8 cm. The WHO median for 12-month boys is 75.7 cm: z-score about 0, 50th centile. Average length, reassuring.
Example 2. A 36-month-old girl measured standing at 87.1 cm. The WHO median for 36-month girls is about 95.1 cm; the z-score works out at -2.1, around the 1.8th centile: stunted by WHO definition. This needs assessment of diet, chronic disease and the growth trend, not just reassurance.
Example 3. A 20-month-old boy measured standing at 82.0 cm. The calculator adds the 0.7 cm correction, comparing 82.7 cm against the recumbent-length median of about 84.2 cm: z-score about -0.5, near the 30th centile. Without the correction the result would look nearly a full centile band lower.
When a low or falling centile needs action
Act promptly when the centile is falling across lines, when height-for-age is below -2 with no familial explanation, when weight is also faltering, or when there are symptoms of chronic disease: recurrent infections, chronic diarrhoea, pallor, developmental concerns. Investigations typically start with diet history, review of chronic illness and medications (including inhaled steroids at high doses), and basic labs, guided by the history.
Remember that catch-up growth is possible when the cause is found and treated, particularly in the first two years. Growth hormone deficiency, hypothyroidism and coeliac disease are all treatable causes of a falling height centile that should not be missed. The chart is the screening tool; the history and examination decide what happens next.
Key takeaways
- Height-for-age reflects chronic growth; it is the indicator for stunting (below -2 z-scores).
- Measure under-2s lying down and over-2s standing; apply the 0.7 cm correction when technique and reference disagree.
- A steady centile, even if low, usually means normal velocity; a falling centile needs investigation.
- Adjust expectations for parental heights; short parents often have healthy short children.
- Stunting's critical window is the first 1,000 days; catch-up is most achievable early.
Frequently asked questions
My child is on the 4th centile for height but both parents are short. Is that a problem?
Probably not. Children tend to grow toward their genetic potential, and the child of two short parents tracking steadily on a low centile is usually healthy. What matters is the trend: steady tracking along the 4th centile is reassuring, while falling from the 25th to the 4th is not. Discuss the mid-parental height target with your clinician for a personalised expectation.
Why did my child's centile drop at age 2?
The commonest benign cause is the switch from lying length to standing height without the 0.7 cm correction: standing reads lower, so the centile appears to fall. If the measurement technique was handled correctly and the fall is real and persistent across re-measurement, then it deserves the same assessment as any falling centile.
Can a stunted child catch up?
Yes, if the underlying cause is identified and treated, especially in the first two years of life. Treating hypothyroidism, coeliac disease or chronic undernutrition can produce striking catch-up growth. After prolonged stunting the potential for full catch-up diminishes, which is why early detection matters.
Is it true that height cannot be increased after puberty?
Essentially yes for natural growth: once the growth plates fuse at the end of puberty, no diet, exercise or supplement adds height. Claims to the contrary are marketing, not medicine. The time to influence height is during childhood, through nutrition, health and treatment of any growth-slowing condition.
How is this different from the weight-for-age calculator?
Weight-for-age is a composite screen that cannot distinguish a short, well-proportioned child from a thin one. Height-for-age isolates linear growth and identifies stunting. Use them together: low weight-for-age with normal height-for-age points toward wasting; low height-for-age with normal weight-for-length points toward stunting.