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Child Growth Lab

Pediatric growth calculators for WHO and CDC references, BMI, growth change, corrected age, and family-height context.

Two measurements · Height change

Height Velocity Calculator for Children

Enter two height measurements and their dates to calculate your child's recorded height change and annualized height velocity in cm/year and in/year.

Free · no account · calculations run in the browser · measurements are not saved as child health records

Step 1 · Measurement setup

Choose units and height method

Changing units clears all measurement values.

Required only when you submit a height or length pair. Use the same method on both dates.

To calculate height velocity, enter height or length on both dates. Weight is optional. Enter weight on both dates if you also want to calculate recorded weight change.

Earlier measurement
Later measurement
Measurement guidance
  • Use two different dates and complete both sides of a matching height/length pair, weight pair, or both.
  • Use the same standing-height or recumbent-length method on both dates. Do not mix one lying-down length with one standing height. This calculator does not apply the CDC SAS 0.8 cm method conversions: the contract adds 0.8 cm to standing height measured before 24 months and subtracts 0.8 cm from recumbent length measured at 24 months or older.
  • Fewer than 6 complete calendar months between height or length measurements gets a caution; annualized rates are mathematical scaling, not predictions.
  • WHO publishes separate infant velocity standards for defined intervals. This page does not load those tables or calculate a WHO velocity percentile.
  • For accurate inputs, use consistent equipment and conditions. Do not mix a lying-down length with a standing height or adjust a clinical record yourself.

Height velocity is the primary calculation. A complete weight pair can also be calculated separately. Complete at least one matching pair: both height/length measurements, both weight measurements, or both.

The broad positive-value limits are technical input protections intended to catch likely entry or unit errors. They are not normal ranges or diagnostic limits.

Use the same height or length method on both dates. Weight on both dates can also give a separate weight-change result. The result is not a percentile, normal range, diagnosis, or prediction. This calculator reports arithmetic change only. It does not calculate WHO infant growth-velocity percentiles.

What this Height Velocity Calculator shows

Height velocity is the rate of change between two dated height or length measurements. You see the recorded change, elapsed interval, and annualized rate in cm/year and in/year. The two-point view shows only the measurements entered, not a future path.

To compare an attained height or weight with an age reference instead, use the Child Growth Chart Calculator. The companion guide below explains velocity and its interpretation in more depth.

Worked example: height velocity

Earlier height
120.0 cm on January 1, 2025
Later height
126.0 cm on January 1, 2026
Elapsed time
365 days
Recorded height change
+6.0 cm
Annualized height velocity
about 6.0 cm/year or approximately 2.4 in/year

This is an arithmetic rate between these two measurements, not a prediction of how much the child will grow next year.

How to calculate height velocity

Enter the earlier date and measurement first, then the later date and measurement. Complete both height or length measurements to calculate height velocity. Use the same units and measurement method on both dates.

Recorded change is the later measurement minus the earlier measurement. The height or length rate divides that change by exact elapsed days expressed as 365.25-day years. Weight is also shown per 30.4375-day average month.

Annualizing is a mathematical conversion, not a forecast that the same change will continue for a full year. Technical constants and canonical Metric inputs remain in the result’s collapsed calculation details.

Why measurement interval matters

For height or length, this page counts complete calendar months. AAP guidance advises against placing too much emphasis on velocity calculated over less than 6 months because short-term variation and measurement differences can dominate the result. Exactly 6 calendar months does not trigger the warning.

How to measure consistently

Use the same reliable equipment, similar clothing conditions, and the same height or length method. Record dates carefully. For standing height, remove shoes and use a flat wall and firm floor; for weight, use a stable scale on a firm surface.

Do not compare recumbent length with standing height as the same pair. The CDC SAS contract adds 0.8 cm to standing height measured before 24 months and subtracts 0.8 cm from recumbent length measured at 24 months or older. This calculator performs neither conversion and does not infer age or method. Do not adjust a clinical record yourself; if the method changed, an appropriate healthcare professional should decide how to handle it.

Optional weight change calculation

You can also enter weight on both dates to calculate recorded weight change and arithmetic monthly and yearly rates, with or without a height pair.

Weight example: January 1 to July 1, 2025 is 181 days and exactly 6 complete calendar months. A change from 24.0 kg to 25.2 kg is +1.2 kg, approximately +0.20 kg/month and +2.42 kg/year. A height pair over the same dates would not receive the under-6-month warning.

What the result cannot tell you

The arithmetic has no pediatric chart age band, but it cannot define normal or abnormal growth, diagnose a condition, predict future growth, or recommend treatment. Age, puberty, health history, family pattern, and a longer accurate measurement series can change clinical interpretation.

What a lower later measurement means

A lower later height, length, or weight remains visible as a recorded decrease. First recheck dates, units, equipment, posture or clothing, and measurement method. The calculator does not infer a medical cause. Discuss an accurate, unexpected pattern with a healthcare professional if you remain concerned.

Babies and WHO velocity standards

WHO publishes actual infant weight-velocity and length-velocity standards for defined early-childhood intervals. Weight standards include 1-month increments from birth to 12 months and 2–6-month increments through 24 months; length standards use 2–6-month increments through 24 months.

This page does not load or implement those WHO velocity tables, z-scores, or percentiles. An arbitrary two-date annualized rate is not a WHO percentile. For attained growth percentiles under age 2, use the WHO Baby Growth Calculator; that page is not a velocity-percentile calculator.

Limitations

  • Measurement and date errors flow directly into the calculated change and rate.
  • Annualizing can magnify small differences and does not predict future growth.
  • The tool does not provide normal ranges, diagnostic thresholds, or treatment advice.
  • It does not calculate CDC or WHO velocity percentiles.
  • Both height or length measurements must use the same method; do not directly compare recumbent length with standing height.
  • The calculator does not apply the CDC SAS 0.8 cm conversions or support self-adjusting a clinical record when measurement methods change.

Helpful context

Frequently asked questions

How do I calculate height velocity?

Enter an earlier height and date, then a later height and date, using the same measurement method. The calculator reports recorded height change and annualized height velocity in cm/year and in/year. It does not decide whether the result is normal.

How far apart should height or length measurements be?

AAP guidance says the earlier height or length is ideally at least 6 months before the later one. This page warns when fewer than 6 complete calendar months have passed but still shows the arithmetic.

Why can a short interval be misleading?

Small differences in posture, equipment, time, or technique can be large compared with the true change over a short interval. Annualizing magnifies that difference and does not predict the next year.

Does this tell me whether my child’s growth is normal?

No. It does not apply normal or abnormal thresholds. Clinical interpretation may consider age, puberty, health history, accurate repeated measurements, and the appropriate growth reference.

What if the later height or length is lower?

The decrease remains visible. Recheck dates, units, posture, shoes, equipment, and whether both measurements used the same lying-down or standing method. The calculator does not infer a cause.

What if the later weight is lower?

First recheck dates, units, clothing, food or drink timing, the scale, and measurement conditions. It may be a real recorded change, but this calculator does not label a cause or diagnosis.

Can I compare lying-down length with standing height?

No. Use the same method for both dates. The CDC SAS contract adds 0.8 cm to standing height measured before 24 months and subtracts 0.8 cm from recumbent length measured at 24 months or older. This calculator performs neither conversion. Do not adjust a clinical record yourself; if the method changed, an appropriate healthcare professional should decide how to handle it.

Is growth velocity the same as a percentile?

No. A velocity is a rate between two observations. A percentile compares a measurement or interval with a defined reference. This calculator provides no velocity percentile.

Does this calculator use WHO infant velocity standards?

No. WHO publishes separate weight- and length-velocity standards for specific early-childhood intervals. This page does not load those tables or calculate a WHO velocity z-score or percentile.

Does this site save the measurements?

Calculator inputs are processed in your browser and are not saved as a child health record or sent to an external calculation service.

References

Understand this result

What Is Growth Velocity in Children?

Understand arithmetic change between two dated measurements and why it is not a diagnosis or velocity percentile.