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Reference{{ resultsReady ? weightAgeHeroSourceLabel : '—' }} Lookup age{{ resultsReady ? `${computation.values.age_used_months.toFixed(1)} mo` : '—' }} Weight{{ resultsReady ? `${measurement} ${measurement_unit}` : '—' }}
Choose the sex recorded for the child growth reference.
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months
Use a recent measured weight and confirm the scale unit.
Hybrid is the neutral default; pin a source only when the review protocol requires it.
Off is neutral; use correction only when it is part of the child’s follow-up workflow.
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Forty weeks applies no correction.
weeks
The default 24-month stop leaves the result unchanged while correction is off.
months
The default is the 5th percentile; changing it adjusts only the local alert lane.
percentile
The default is the 95th percentile; changing it adjusts only the local alert lane.
percentile
Three months is the neutral starting interval before review cues shorten it.
months
Balanced is the neutral follow-up stance.
Routine is neutral and leaves the baseline timing unchanged.
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How to use this screening result

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A child's weight has to be read against age and sex before it has useful growth-chart meaning. Eight kilograms can occupy a very different position for a young infant than for a toddler. Weight-for-age supplies that comparison by placing one measurement within a same-age, same-sex reference distribution.

A percentile describes rank, not a percentage of an ideal weight. The 25th percentile means that about one quarter of the reference distribution is below that weight at the same age and sex. It does not mean the child has reached 25% of a target, and the 50th percentile is not a goal every child should approach.

Useful forNot enough for
Placing one weight on an age- and sex-specific reference.Deciding whether weight is appropriate for height or length.
Tracking movement across repeated, accurate measurements.Diagnosing undernutrition, overweight, illness, or a feeding problem by itself.
Identifying a point that deserves review with the child's history.Replacing clinical assessment, measurement technique, or a complete growth record.

Reference choice can shift the plotted position without any change in the child. In U.S. practice, World Health Organization (WHO) standards are recommended from birth to age 2 and Centers for Disease Control and Prevention (CDC) charts from age 2 onward. The two sets were built from different populations and methods, so extra care is needed around the 24-month handoff.

For a child born preterm, corrected age may be used for a limited early period when that matches the clinician's follow-up approach. Correction moves the age used for the lookup; it does not alter the measured weight. Gestational age, illness, hydration, edema, puberty, specialized growth conditions, and the child's own earlier curve all affect interpretation.

Health note: This result is an educational screening aid, not a diagnosis or treatment recommendation. Discuss very low, very high, rapidly changing, premature-infant, or otherwise concerning growth with a qualified health professional.

How to Use This Tool:

Use a current, accurate weight and the child's recorded age and sex, then choose the applicable growth reference.

  1. Choose the Sex used by the growth reference, then enter chronological Age from 0 to 240 months.
  2. Enter the measured Weight and select kg or lb. Use a recent measurement from suitable, maintained equipment.
  3. Choose the Reference pathway. Hybrid uses WHO below 24 months and CDC from 24 months; WHO-first continues WHO through 60 months; CDC uses CDC rows throughout the supported range.
  4. Turn on Correct age for prematurity only when corrected age belongs in the child's review plan, then enter gestational age and the stop point.
  5. Leave alert and follow-up settings at their defaults unless you are applying a defined local review policy. They change screening notes and suggested timing, not the calculated percentile.
  6. Check the percentile, z-score, age used, and reference source before interpreting the chart position.

Interpreting Results:

Read Percentile with Z-score, Age used for lookup, and the named reference. A point near the middle of the distribution is not automatically healthy, and an outer percentile is not automatically a diagnosis. Repeated measurements taken accurately and interpreted with length or height, health history, and developmental context are more informative than one point.

The configurable low and high alert percentiles are local screening lanes. They do not change WHO or CDC reference data and should not be presented as universal clinical cutoffs. The generated follow-up interval is a repo-authored planning cue; a clinician's judgment and the child's circumstances take priority.

Technical Details:

WHO 2006 and CDC 2000 weight-for-age tables provide age- and sex-specific LMS parameters. M is the median, S controls spread, and L is a Box-Cox power that accounts for skew. Decimal ages use linear interpolation between adjacent LMS rows before the weight is converted to a z-score.

Lookup Core

PathwayReference rule
HybridWHO when age used is below 24 months; CDC at 24 months and older.
WHO-firstWHO through and including 60 months; CDC continuation above 60 months.
CDCCDC infant rows below 24 months and CDC child rows from 24 through 240 months.

When correction is active, the age used subtracts the number of weeks short of 40 weeks' gestation, converted with 4.348125 weeks per month. Correction applies only while chronological age is less than or equal to the selected stop point.

Acorrected = max(0, Achronological − 40−Gweeks4.348125 )

Formula Core

The LMS equation converts weight X in kilograms to a z-score. When L is effectively zero, the logarithmic form is used.

z= (XM)L−1 LS
z=ln(XM)Swhen L = 0

The percentile is the standard normal cumulative probability for z, multiplied by 100 and displayed within 0.1 to 99.9. Pounds are divided by 2.2046226218 before lookup. Display rounding does not feed back into the LMS calculation.

Rule Core

Rule familyExact boundaries
WHO display categoriesz < −3 severe underweight; −3 ≤ z < −2 underweight; −2 ≤ z ≤ 2 expected; 2 < z ≤ 3 high; z > 3 very high.
CDC display categoriesPercentile < 3 very low; 3 to < 5 low; 5 to < 95 typical; 95 to < 97 high; ≥ 97 very high.
Custom alert lanesBelow when percentile < low; above when percentile > high; equality stays inside and is marked near the boundary.
Near-boundary noteShown when the percentile is within 2 percentage points of either configured alert boundary.

Follow-up timing begins with the chosen baseline. Priority categories cap it at 0.5 month and watch categories at 1.5 months; a point within 1 percentage point of an alert boundary caps it at 1 month, and within 2 points caps it at 2 months. Active corrected age also caps it at 2 months. Follow-up stance and urgency then multiply that interval, which is limited to 0.25 through 12 months and rounded to the nearest quarter month. These rules are planning logic, not a published clinical schedule.

Limitations:

Weight-for-age omits length or height, body composition, pubertal stage, and individual medical context. The reference tables represent populations, not a personal growth prescription.

  • Measurement error, clothing, feeding, hydration, edema, and scale calibration can move a percentile.
  • Abrupt lane changes near 24 months may reflect the WHO-to-CDC switch as well as real growth.
  • Specialized conditions may require condition-specific charts or clinical interpretation.
  • Corrected age should follow the child's care plan rather than being enabled automatically.

References: