Use this calculate newborn weight percentile tool to compare a newborn's birth weight with standard growth chart percentiles by gestational age and sex. Enter the birth weight, gestational age, and select sex to instantly see the percentile along with Z-score, deviation from median, and expected reference weights.
Newborn Weight Percentile Calculator
Enter the measured birth weight in grams (typical full-term range 2500-4500 g).
Please enter a valid birth weight between 300 and 6000 grams.
Gestational age at delivery in completed weeks (e.g., 39.0).
Please enter a valid gestational age between 22 and 42 weeks.
Male
Female
Growth references vary slightly by sex; choose the newborn's sex.
Please select a sex.
Percentile: 50th
Z-Score:0.00
Expected Median Weight:0 g
Difference from Median:0 g
Reference SD:0 g
Formula:Percentile uses LMS method with Z = [(weight/M)^L – 1]/(L×S) and percentile = Φ(Z).
Blue line: median expected weight; Green line: entered weight plotted across gestational ages.
Typical Reference Weights by Gestational Age
Gestational Age (weeks)
10th % (g)
50th % (g)
90th % (g)
What is calculate newborn weight percentile?
calculate newborn weight percentile describes the process of positioning a newborn's birth weight on a standardized growth distribution for a specific gestational age and sex. Parents, pediatricians, and neonatal teams use calculate newborn weight percentile to gauge whether a baby is small for gestational age, appropriate for gestational age, or large for gestational age. A common misconception is that calculate newborn weight percentile is a fixed score; in reality it changes with gestational age, sex, and measurement accuracy.
calculate newborn weight percentile Formula and Mathematical Explanation
The core approach for calculate newborn weight percentile relies on the LMS growth chart method. For each gestational week, three parameters—L (skewness), M (median), and S (coefficient of variation)—define the weight distribution. The Z-score is calculated as:
Z = ((weight / M)L – 1) / (L × S). The percentile equals the cumulative probability Φ(Z) converted to a percentile scale. calculate newborn weight percentile uses this to map raw weight to a percentile.
Variables for calculate newborn weight percentile
Variable
Meaning
Unit
Typical Range
L
Lambda (power to normalize skew)
unitless
-2 to 2
M
Median reference weight
grams
500 to 4000
S
Coefficient of variation
unitless
0.05 to 0.2
weight
Observed birth weight
grams
300 to 6000
Φ(Z)
Normal cumulative probability
percent
0 to 100
Practical Examples (Real-World Use Cases)
Example 1: Full-term male
Inputs: weight 3300 g, gestational age 39.5 weeks, sex male. The calculate newborn weight percentile result is about the 55th percentile. Interpretation: the baby is slightly above median, consistent with appropriate for gestational age without clinical concern.
Example 2: Late preterm female
Inputs: weight 2200 g, gestational age 35 weeks, sex female. The calculate newborn weight percentile returns near the 35th percentile. Interpretation: mild low weight but still within appropriate-for-gestational-age range; closer monitoring and feeding support may be advised.
How to Use This calculate newborn weight percentile Calculator
Enter the birth weight in grams, the gestational age in weeks, and select sex. The calculate newborn weight percentile tool immediately updates the percentile, Z-score, median reference weight, and difference from median. Review the chart to see how the baby's weight compares to median across nearby gestational ages. Use the copy results button to share calculate newborn weight percentile outputs with care teams.
Key Factors That Affect calculate newborn weight percentile Results
calculate newborn weight percentile is influenced by gestational age accuracy, fetal growth restriction risks, maternal health, placental function, altitude, and measurement timing. Additional financial planning factors linked to calculate newborn weight percentile include healthcare costs for neonatal care, insurance deductibles, parental leave budgeting, inflation-adjusted medical expenses, and potential nutritional supplementation fees. Accurate scales, standardized weighing conditions, and correct dating from early ultrasounds make calculate newborn weight percentile more reliable.
Frequently Asked Questions (FAQ)
Does calculate newborn weight percentile change after birth? Yes, weight changes daily; recalculate with each measurement.
Is calculate newborn weight percentile different for twins? Multiples often follow separate curves; use twin-specific references if available.
What if gestational age is uncertain? Use the best dating method; uncertainty can shift calculate newborn weight percentile notably.
Can I use pounds instead of grams? Convert to grams before using this calculate newborn weight percentile tool for accuracy.
Are charts the same worldwide? Regional charts differ; this calculate newborn weight percentile uses generalized references.
What percentile is concerning? Below 10th or above 90th may prompt closer evaluation, but clinical context matters.
How often should I recalc? At each weight check to track trends with calculate newborn weight percentile.
{related_keywords} – Compare percentile changes over time with newborn development guides.
{related_keywords} – Learn about feeding plans aligned with calculate newborn weight percentile.
{related_keywords} – Review pediatric visit schedules and budgeting tips.
{related_keywords} – Understand hospital cost planning based on calculate newborn weight percentile risk.
{related_keywords} – Access parental leave calculators connected to newborn care needs.
var growthData = {
male: [
{w:22,M:520,L:-0.12,S:0.17},
{w:24,M:650,L:-0.1,S:0.16},
{w:26,M:900,L:-0.08,S:0.15},
{w:28,M:1150,L:-0.05,S:0.14},
{w:30,M:1400,L:-0.04,S:0.13},
{w:32,M:1750,L:-0.03,S:0.12},
{w:34,M:2150,L:-0.02,S:0.115},
{w:35,M:2450,L:-0.015,S:0.11},
{w:36,M:2750,L:-0.01,S:0.105},
{w:37,M:3050,L:-0.008,S:0.1},
{w:38,M:3200,L:-0.006,S:0.095},
{w:39,M:3350,L:-0.005,S:0.09},
{w:40,M:3450,L:-0.004,S:0.09},
{w:41,M:3550,L:-0.004,S:0.092},
{w:42,M:3600,L:-0.004,S:0.095}
],
female: [
{w:22,M:500,L:-0.12,S:0.18},
{w:24,M:620,L:-0.1,S:0.17},
{w:26,M:860,L:-0.08,S:0.16},
{w:28,M:1100,L:-0.06,S:0.15},
{w:30,M:1350,L:-0.05,S:0.14},
{w:32,M:1650,L:-0.04,S:0.13},
{w:34,M:2050,L:-0.03,S:0.12},
{w:35,M:2320,L:-0.025,S:0.115},
{w:36,M:2620,L:-0.02,S:0.11},
{w:37,M:2900,L:-0.015,S:0.105},
{w:38,M:3050,L:-0.012,S:0.1},
{w:39,M:3200,L:-0.01,S:0.095},
{w:40,M:3300,L:-0.009,S:0.095},
{w:41,M:3380,L:-0.009,S:0.097},
{w:42,M:3450,L:-0.009,S:0.1}
]
};
function findRef(sex, gestation) {
var arr = growthData[sex];
if (!arr) { return null; }
if (gestation = arr[arr.length-1].w) { return arr[arr.length-1]; }
for (var i=0;i=a.w && gestation0){prob=1-prob;}
return prob;
}
function updateTable(){
var body=document.getElementById("referenceTableBody");
var sex=document.getElementById("sex").value;
var arr=growthData[sex];
var html="";
for(var i=0;i<arr.length;i++){
var m=arr[i].M;
var sd=arr[i].S*arr[i].M;
var p10=Math.round(m + sd*invNorm(0.1)*1);
var p90=Math.round(m + sd*invNorm(0.9)*1);
html+="
"+arr[i].w.toFixed(1)+"
"+p10+" g
"+Math.round(m)+" g
"+p90+" g
";
}
body.innerHTML=html;
}
function invNorm(p){
var a1=-39.6968302866538,a2=220.946098424521,a3=-275.928510446969;
var a4=138.357751867269,a5=-30.6647980661472,a6=2.50662827745924;
var b1=-54.4760987982241,b2=161.585836858041,b3=-155.698979859887;
var b4=66.8013118877197,b5=-13.2806815528857;
var c1=-0.00778489400243029,c2=-0.322396458041136,c3=-2.40075827716184;
var c4=-2.54973253934373,c5=4.37466414146497,c6=2.93816398269878;
var d1=0.00778469570904146,d2=0.32246712907004,d3=2.445134137143;
var d4=3.75440866190742;
var plow=0.02425,phigh=1-plow;
var q,r,x;
if(p6000){
document.getElementById("weightError").style.display="block";
valid=false;
}else{
document.getElementById("weightError").style.display="none";
}
if(isNaN(gest) || gest42){
document.getElementById("gestationError").style.display="block";
valid=false;
}else{
document.getElementById("gestationError").style.display="none";
}
if(sex!=="male" && sex!=="female"){
document.getElementById("sexError").style.display="block";
valid=false;
}else{
document.getElementById("sexError").style.display="none";
}
if(!valid){return;}
var ref=findRef(sex,gest);
var L=ref.L;
var M=ref.M;
var S=ref.S;
var z=0;
if(L!==0){
z=((Math.pow(weight/M,L))-1)/(L*S);
}else{
z=Math.log(weight/M)/S;
}
var percentile=Math.round(cdfNormal(z)*1000)/10;
if(percentile100){percentile=100;}
document.getElementById("zScore").textContent=z.toFixed(2);
document.getElementById("medianWeight").textContent=Math.round(M)+" g";
document.getElementById("diffMedian").textContent=Math.round(weight – M)+" g";
document.getElementById("sdValue").textContent=Math.round(S*M)+" g";
document.getElementById("mainResult").textContent="Percentile: "+percentile.toFixed(1)+"th";
drawChart(weight,sex);
}
function resetForm(){
document.getElementById("weight").value=3200;
document.getElementById("gestation").value=39;
document.getElementById("sex").value="male";
calculateAll();
}
function copyResults(){
var main=document.getElementById("mainResult").textContent;
var z=document.getElementById("zScore").textContent;
var median=document.getElementById("medianWeight").textContent;
var diff=document.getElementById("diffMedian").textContent;
var sd=document.getElementById("sdValue").textContent;
var assumptions="Gestational age-specific LMS method for calculate newborn weight percentile.";
var text=main+"\nZ-Score: "+z+"\nMedian Weight: "+median+"\nDifference from Median: "+diff+"\nReference SD: "+sd+"\n"+assumptions;
if(navigator.clipboard && navigator.clipboard.writeText){
navigator.clipboard.writeText(text);
}else{
var temp=document.createElement("textarea");
temp.value=text;
document.body.appendChild(temp);
temp.select();
document.execCommand("copy");
document.body.removeChild(temp);
}
}
function drawChart(weight,sex){
var c=document.getElementById("growthChart");
var ctx=c.getContext("2d");
ctx.clearRect(0,0,c.width,c.height);
var arr=growthData[sex];
var pad=50;
var w=c.width – pad*2;
var h=c.height – pad*2;
var minW=400;
var maxW=4000;
var minG=22;
var maxG=42;
for(var i=0;i<arr.length;i++){
if(arr[i].MmaxW){maxW=arr[i].M+200;}
}
var scaleX=function(g){return pad + (g – minG)/(maxG – minG)*w;};
var scaleY=function(val){return c.height – pad – (val – minW)/(maxW – minW)*h;};
ctx.strokeStyle="#d6dde6″;
ctx.lineWidth=1;
for(var g=22;g<=42;g+=2){
var x=scaleX(g);
ctx.beginPath();
ctx.moveTo(x,pad/2);
ctx.lineTo(x,c.height – pad/2);
ctx.stroke();
ctx.fillStyle="#5c6b7a";
ctx.fillText(g+"w",x-10,c.height – pad/2 +14);
}
ctx.fillStyle="#5c6b7a";
ctx.fillText("Weight (g)",10,pad-10);
ctx.save();
ctx.translate(c.width – pad +10,pad);
ctx.rotate(Math.PI/2);
ctx.restore();
ctx.beginPath();
for(i=0;i<arr.length;i++){
var x=scaleX(arr[i].w);
var y=scaleY(arr[i].M);
if(i===0){ctx.moveTo(x,y);}else{ctx.lineTo(x,y);}
}
ctx.strokeStyle="#004a99";
ctx.lineWidth=3;
ctx.stroke();
ctx.beginPath();
for(i=0;i<arr.length;i++){
x=scaleX(arr[i].w);
y=scaleY(weight);
if(i===0){ctx.moveTo(x,y);}else{ctx.lineTo(x,y);}
}
ctx.strokeStyle="#28a745";
ctx.lineWidth=2;
ctx.setLineDash([6,4]);
ctx.stroke();
ctx.setLineDash([]);
var gest=parseFloat(document.getElementById("gestation").value);
var px=scaleX(gest);
var py=scaleY(weight);
ctx.fillStyle="#28a745";
ctx.beginPath();
ctx.arc(px,py,6,0,Math.PI*2);
ctx.fill();
}
updateTable();
calculateAll();