Frequently Asked Questions
Common questions about the baby growth percentile calculator. Reach us at comsamo84@gmail.com for more.
Q1Is this calculator a medical diagnosis?
No. It is a reference indicator based on the WHO and KCDC 2017 growth standards. Always confirm any concern with a pediatrician.
Q2How are WHO and KCDC standards different?
Since 2017, Korea (KCDC / Korean Pediatric Society) adopted the WHO standards verbatim for 0-24 months, so WHO and KCDC are effectively the same reference in that window. After 24 months KCDC uses Korean-specific data, but this tool focuses on 0-24 months.
Q3What percentile is considered "normal"?
The reference window is typically the 3rd-97th percentile. The 25th-75th is the central band. A single reading below the 3rd or above the 97th warrants a double-check, but the trend (tracking a single curve) matters more than a single number.
Q4What is a Z-score?
A Z-score measures how many standard deviations a value is from the median. Z=0 is the 50th; Z ≈ ±1.88 maps to the 3rd/97th. Clinically, Z ≤ -2 or Z ≥ +2 is a common "look closer" threshold.
Q5Where is my data stored?
Baby info and measurements live only in your browser's localStorage. Nothing is sent to a server, so data persists on the same device and browser. Clearing browser data clears the history.
Q6Why only up to 24 months?
The WHO standard for 0-24 months uses recumbent length, and Korea uses the same. After 24 months, stature (standing height) and Korean-specific data apply — a different chart. We may extend this tool later.
Q7My baby was born early — how do I use this?
For babies born 3+ weeks early, use corrected age (from the due date) until about 24 months to avoid underestimating. Since this calculator computes calendar age, you can simply enter the due date as the birth date to get a corrected-age result.
Q8My baby is a twin — should the standard be different?
Twins tend to be lighter at birth and may grow at a slightly different pace, but WHO does not publish a twin-specific chart. Clinicians use the same reference while accounting for gestational age, birth weight, and corrected age. Individualized assessment by a pediatrician is especially important.
Q9My baby's weight is high but length is low — overweight?
Weight-for-length matters more than weight alone. This tool shows each measurement separately, so interpret overweight/underweight with your pediatrician using a weight-for-length chart. Weight-for-length above the 85th percentile is a common flag.
Q10Is it a problem if the percentile suddenly changes?
A single outlier can be measurement error - re-check in 2+ weeks with the same scale and time of day. If a baby crosses 2+ major bands consistently (e.g. P75 → P25), see a pediatrician, especially for flat or dropping weight.
Q11Do breastfed and formula-fed babies grow differently?
The WHO standards are built on healthy, primarily breastfed cohorts across countries. Formula-fed babies sometimes gain a bit faster after 3-6 months, but both international and Korean guidelines interpret growth against the same WHO reference.
Q12How do I measure accurately?
Weight: fully undressed on an infant scale (0.01 kg). Length: recumbent, crown to heel with legs straight. Head circumference: greatest circumference above the brow and occiput, averaged over 3 readings. Home measurements are noisier than clinic ones — combine with well-baby check-ups.
Q13Is this tool free?
Yes, completely free. We cover costs via ads and limited affiliate links. No measurement data is collected.
Q14Sources and last update?
WHO Child Growth Standards (2006) · KCDC 2017 Korean Growth Charts · AAP Bright Futures. Last reviewed: 2026-04-19.