Growth Velocity Calculator

Reference sex:

Choose the child's reference curve: Female or Male.

Visit metric:

Pick Height with cm/in or Weight with kg/lb; use the same unit for every visit row.

{{ profile.visitLabel }}:

Enter one visit per line as age_months,value; example {{ visitRowsPlaceholder.split('\n')[0] }}. Duplicate ages keep the latest row.

Expected range model:

Hybrid is the default for series crossing the WHO-to-CDC handoff near age 24 months.

Expected-growth stage:

Auto uses each interval midpoint; fixed presets apply one stage to the whole series.

Velocity alert sensitivity:

Enter 0.80 to 1.20; 1.00 keeps the baseline screen.

Streak alert threshold:

Use an integer from 1 to 4; default 2 requires a repeat.

intervals

Risk tolerance:

Conservative flags earlier; Tolerant waits for stronger repeated signals.

Guidance follow-up interval:

Enter 0.5 to 12 months in 0.5-month steps.

months

Intervention urgency:

Routine keeps baseline timing; Priority and Urgent shorten follow-up suggestions.

Catch-up priority:

Choose Linear for height-led review or Weight for weight-gain review; calculations stay unchanged.

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Section	Signal	Value	Detail
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Priority	Recommendation	Rationale	Timeline	Copy
{{ row.priority }}	{{ row.recommendation }}	{{ row.rationale }}	{{ row.timeline }}
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A single point on a growth chart can miss the story between visits. A child may still plot inside a familiar percentile band while the pace of height gain has slowed, or a weight curve may jump because one interval was unusually short, an illness resolved, or measurement technique changed. Growth velocity adds the time interval to the measurement, so the question becomes how much height or weight changed per year rather than where the latest dot sits.

The idea is simple, but the interpretation is not one-size-fits-all. Infants grow quickly, toddlers slow down, school-age children usually have steadier linear growth, and puberty can bring a faster height phase before growth tapers. Weight velocity follows its own rhythm because feeding, hydration, illness, activity, and body composition can change faster than height. That is why the same annualized number can be ordinary at one age and worth rechecking at another.

Growth velocity: The change in height or weight divided by the time between two visits, usually expressed per year.
Percentile drift: The movement from one age- and sex-based percentile position to another across the visit series.
Expected band: A practical comparison range for the child's age stage and measurement type, not a diagnosis by itself.

Four growth velocity intervals compared with an expected range, with one low and one high interval highlighted

A useful velocity review starts with repeated measurements taken in a comparable way. Recumbent length and standing height are not identical, infant weight can move quickly around feeding or illness, and a small height error can become a large annualized rate when visits are close together. The interval is part of the measurement, not just a date label.

The same metric should be followed across the whole series, either height or weight.
Visits spaced about 6 to 12 months apart usually give a steadier read than very short intervals.
Percentile movement matters most when it repeats or crosses major bands, not when one point shifts slightly.
Rapid gain and slow gain both need context from age, puberty timing, illness, nutrition, and measurement quality.

This information is educational and supports growth review only. It does not replace standardized measurement, formal growth-chart interpretation, diagnosis, or treatment decisions.

How to Use This Tool:

Start with the cleanest visit series, then use the advanced controls only when you need to test a different review posture.

Choose Reference sex. This sets the sex-specific reference median, percentile drift, z-score, and height floor checks used in the review.
Set Visit metric to Height or Weight, then choose the matching unit. Keep every visit row in the same metric and unit family.
Enter Visit data rows as one visit per line, such as 6,65.1 or 24,12.0. The first number is age in months and the second is the height or weight value.
Pick an Expected range model. Use Hybrid continuity profile when the series crosses the 24-month WHO-to-CDC handoff unless you have a reason to emphasize one reference set.
Leave Expected-growth stage on Auto by interval age midpoint for the baseline pass. Fixed infant, toddler, childhood, or adolescent presets apply one stage multiplier across the whole series.
Keep Velocity alert sensitivity at 1.00x and Streak alert threshold at 2 unless you are intentionally tightening or loosening the low/high band and sustained-pattern rule.
Use Risk tolerance, Guidance follow-up interval, Intervention urgency, and Catch-up priority to shape follow-up wording. These controls do not change the interval calculations.
Read Velocity Review Metrics first, then check Visit Source Ledger, Interval Review Table, Velocity Review Lens, Velocity Follow-Up Guidance, Velocity Band Chart, and the growth path chart when the headline result needs support.

If the page shows a row-format error, fix that row before interpreting the result. Ages must be from 0 to 240 months, values must be positive numbers, and duplicate ages keep the latest row entered for that age.

Interpreting Results:

Begin with Latest annualized velocity, Latest expected band, and Latest interval status. Those fields say whether the newest interval is below, inside, or above the current age-stage comparison band. Then use Dominant pattern, Pattern alert, Spacing quality, and Review confidence to decide how much weight the headline deserves.

Expected-band hit rate summarizes how many intervals landed inside the expected band.
Latest percentile drift shows the percentile movement from the previous visit to the latest visit.
Net percentile shift compares the first visit with the latest visit across the whole series.
Cumulative velocity delta adds the interval differences from expected pace, so repeated small misses can add up.
Height screen floor appears only for height intervals where an age-based floor check applies.

An Expected latest interval is not the same as a clean growth history. Earlier low intervals, downward percentile drift, low-confidence spacing, or a height floor alert can still make the review worth repeating. A High interval also needs context because catch-up growth, pubertal timing, scale or stadiometer technique, and short spacing can all raise the annualized rate.

Growth velocity interpretation cues
Result pattern	How to read it	Verification cue
Expected latest interval, moderate or high confidence	The newest annualized pace fits the current expected band.	Confirm the visit ledger uses the intended ages, metric, unit, and reference sex.
Low latest interval plus low streak	The slowdown repeats rather than appearing as one isolated interval.	Open `Interval Review Table` and compare each interval with its expected band and spacing label.
Expected latest interval after earlier low values	The newest pace may be recovering, but the full series still matters.	Check `Dominant pattern`, `Net percentile shift`, and `Expected-band hit rate`.
Low-confidence spacing	Annualized rates may be distorted by very short or very long visit gaps.	Repeat with a cleaner 3-to-6-month or 6-to-12-month interval when appropriate.

Technical Details:

Growth velocity is an interval rate. The measurement change is divided by elapsed months and multiplied by 12, so height is displayed as centimeters or inches per year and weight is displayed as kilograms or pounds per year. The expected band is then built from an age-based center rate, an age-stage multiplier, and the selected sensitivity setting.

The WHO, CDC, and hybrid choices shape percentile position, z-score, and reference median-track comparison. The low/expected/high velocity band is a separate screening rule in this calculator, so it should not be read as a direct WHO or CDC velocity standard.

Formula Core:

The first equation annualizes the observed interval. The second equation sets the expected center and classifies the observed value against lower and upper bounds.

\begin{array}{lcl} V & = & \frac{x_{2} - x_{1}}{m_{2} - m_{1}} \times 12 \\ V_{expected} & = & V_{base} (m_{mid}, metric) \times M_{stage} \\ Lower & = & V_{expected} \times (0.70 + (S - 1) \times 0.08) \\ Upper & = & V_{expected} \times (1.40 - (S - 1) \times 0.12) \end{array}

Here x is the height or weight value, m is age in months, V is annualized velocity, m_mid is the interval midpoint age, and S is Velocity alert sensitivity. At 1.00x, the lower bound is 70% of expected and the upper bound is 140% of expected. Values below the lower bound are Low, values above the upper bound are High, and values on either boundary remain Expected.

Expected Rate Rules:

Base expected rates by interval midpoint age
Interval midpoint age	Height base	Weight base
0 to under 12 months	24 cm/year	6.0 kg/year
12 to under 24 months	12 cm/year	3.0 kg/year
24 to under 36 months	8 cm/year	2.2 kg/year
36 to under 60 months	7 cm/year	2.2 kg/year
60 to under 120 months	5.5 cm/year	2.6 kg/year
120 to under 156 months	5.0 cm/year	3.4 kg/year
156 to under 180 months	7.5 cm/year	4.8 kg/year
180 to under 204 months	4.0 cm/year	3.0 kg/year
204 to 240 months	2.2 cm/year	1.7 kg/year

Stage multipliers and spacing categories
Rule area	Current behavior	Interpretation effect
Stage multiplier	Auto chooses infant 1.18, toddler 1.05, childhood 0.92, or adolescent 0.82 by interval midpoint. A fixed preset applies one multiplier to every interval.	The expected center changes before the lower and upper bounds are applied.
Reference profile	WHO, CDC, and hybrid options adjust median and standard deviation values used for percentiles, z-scores, and median-track velocity.	The same observed visit can show different percentile drift around chart transitions.
Streak alert	`Pattern alert` turns on when the longest low or high streak reaches the selected 1-to-4 interval threshold.	Repeated deviation is treated as stronger evidence than one isolated interval.
Height screen floor	Height intervals use a floor from 24 to under 120 months: 5.5 cm/year before 48 months, 5.0 before 72 months, then 4.5 for females or 4.0 for males before 120 months.	A floor alert flags a height-specific recheck cue without changing the low/expected/high band.

Spacing categories for growth velocity intervals
Interval span	Spacing label	Meaning
Under 3 months	Too short	Most vulnerable to measurement noise after annualizing.
3 to under 6 months	Usable short	Informative, but still more sensitive to small errors.
6 to 12 months	Preferred	Best default window for stable serial comparison.
Over 12 to 18 months	Extended	Usable, but shorter changes may be hidden.
Over 18 months	Long gap	Lower confidence because age stage, health, or puberty may have changed.

For a height interval from 18 months at 80.2 cm to 24 months at 86.0 cm, the observed velocity is (86.0 - 80.2) / (24 - 18) x 12 = 11.6 cm/year. With auto staging, the midpoint is 21 months, the expected center is 12 x 1.05 = 12.6 cm/year, and the default expected band is 8.82 to 17.64 cm/year, so the interval is classified as Expected.

Accuracy and Privacy Notes:

Growth velocity depends on measurement quality. A few millimeters of height difference can meaningfully change a short-interval annualized result, and weight can shift with clothing, scale calibration, fluid status, recent illness, and timing.

Use the same measurement technique and unit family across the series whenever possible.
Treat the output as a screening aid for review, not as a diagnosis or treatment plan.
The visit series is processed in the browser session. Rows are copied or downloaded only when you choose an export action.

Worked Examples:

A height series that recovers toward expected

Rows of 6,65.1, 12,74.6, 18,80.2, and 24,86.0 in centimeters produce a latest interval from 18 to 24 months. Latest annualized velocity is 11.6 cm/year, Latest expected band is 8.82 to 17.64 cm/year, and Latest interval status is Expected. The earlier 6-to-12-month interval was low, so Dominant pattern may still read as recovery rather than an entirely stable history.

Repeated low weight gain

Rows of 24,12.0, 30,12.6, and 36,13.0 in kilograms create two six-month weight intervals. The latest interval is 0.8 kg/year against a 1.62 to 3.23 kg/year expected band, so Latest interval status is Low. With the default two-interval streak threshold, Pattern alert changes to consecutive interval review needed.

Short spacing lowers confidence

Rows of 24,86.0, 25,86.3, and 27,87.4 in centimeters can show an expected latest interval because 6.6 cm/year sits inside the 5.88 to 11.76 cm/year expected band. Both intervals are under three months, so Spacing quality becomes low confidence and the result should be treated as a recheck cue.

A row-format error

A row such as 12 months,74.6 fails because the first two fields must be numeric. Change it to 12,74.6, confirm the row uses the same unit as the rest of the series, and rerun the review before reading Velocity Review Metrics.

FAQ:

How should visit rows be formatted?

Use one numeric visit per line as age_months,value. Commas, spaces, semicolons, tabs, and pipe separators can parse, but the first two fields must be numbers.

Does the WHO, CDC, or hybrid choice change the expected velocity band?

No. It changes percentile context, z-score, and median-track comparison. The expected velocity band comes from the age-stage screening rule and sensitivity setting.

Why can the latest interval be expected while the review still looks concerning?

The newest interval may have returned to the expected band after earlier low intervals, or the full series may still show negative percentile drift, low confidence, or a sustained streak.

Can this diagnose poor growth or rapid weight gain?

No. It summarizes serial measurements and highlights follow-up cues. Diagnosis requires proper measurement, full growth-chart review, medical history, physical exam context, and professional judgment.

Does the visit data leave my browser for calculation?

The calculation runs in the browser session. Visit rows are not uploaded for the growth-velocity calculation, and exports happen only when you copy or download them.

Glossary:

Annualized velocity: The interval change converted to a per-year rate so visits with different spacing can be compared.
Expected band: The lower-to-upper range used to classify an interval as low, expected, or high.
Median-track velocity: The rate implied by the reference median between the same two ages.
Percentile drift: The change in percentile points from one visit to another or from the first visit to the latest visit.
Spacing quality: The confidence label based on whether intervals are very short, preferred, extended, or long.
Pattern alert: The sustained-signal flag that appears when consecutive low or high intervals meet the selected streak threshold.

References:

CDC Growth Charts, Centers for Disease Control and Prevention, September 2, 2024.
Using WHO Growth Standard Charts, Centers for Disease Control and Prevention, March 20, 2024.
WHO child growth standards: growth velocity based on weight, length and head circumference: methods and development, World Health Organization, November 12, 2009.
Growth and Short Stature, Endocrine Society, March 10, 2022.