diff --git a/.nvmrc b/.nvmrc
index 5edcff0..b6a7d89 100644
--- a/.nvmrc
+++ b/.nvmrc
@@ -1 +1 @@
-v16
\ No newline at end of file
+16
diff --git a/src/health_modules/child/zScoreCalculator.js b/src/health_modules/child/zScoreCalculator.js
index a485662..c9ed1fb 100644
--- a/src/health_modules/child/zScoreCalculator.js
+++ b/src/health_modules/child/zScoreCalculator.js
@@ -14,8 +14,8 @@ const anthropometricReference = {
     wfh: {Male: wfh_boys, Female: wfh_girls}
 };
 
-const roundedHeight = (num) =>{
-    return Math.round(num*2)/2;
+const roundedHeight = (num) => {
+    return Math.round(num * 2) / 2;
 };
 
 const getWfaReference = (gender, ageInMonths) => {
@@ -25,7 +25,7 @@ const getWfaReference = (gender, ageInMonths) => {
 
 const getWfhReference = (gender, height) => {
     let wfhReference = _.get(anthropometricReference, ["wfh", gender]);
-    return _.find(wfhReference,(item) => item.x === roundedHeight(height));
+    return _.find(wfhReference, (item) => item.x === roundedHeight(height));
 }
 
 const getHfaReference = (gender, ageInMonths) => {
@@ -33,6 +33,15 @@ const getHfaReference = (gender, ageInMonths) => {
     return _.find(heightForAgeReference, (item) => item.Month === ageInMonths);
 }
 
+function calc_sd(reference, sd) {
+    const {L, M, S} = reference;
+    return M * ((1 + L * S * sd) ^ (1 / L));
+}
+
+function roundToOneDecimal(value) {
+    return Math.round(10 * value) / 10;
+}
+
 /**
  * Uses the LMS formula to calculate zScore.
  *
@@ -45,7 +54,20 @@ const getHfaReference = (gender, ageInMonths) => {
 const calculate = (value, reference) => {
     if (!value || value === 0 || !reference) return undefined;
 
-   return Math.round(10 * (Math.pow(value / reference.M, reference.L) - 1) / (reference.S * reference.L)) / 10;
+    // https://github.com/WorldHealthOrganization/anthro/blob/master/R/z-score-helper.R#L28
+    const sd3pos = calc_sd(reference, 3);
+    const sd3neg = calc_sd(reference, -3);
+    const sd23pos = sd3pos - calc_sd(reference, 2);
+    const sd23neg = calc_sd(reference, 2) - sd3neg;
+
+    let zScore = roundToOneDecimal((Math.pow(value / reference.M, reference.L) - 1) / (reference.S * reference.L));
+
+    if (Math.round(zScore) > 3)
+        zScore = roundToOneDecimal(3 + ((value - sd3pos) / sd23pos));
+    else if (Math.round(zScore) < -3)
+        zScore = roundToOneDecimal(-3 + ((value - sd3neg) / sd23neg));
+
+    return zScore;
 };
 
 const calculateZScore = (gender, ageInMonths, weight, height) => {
@@ -53,8 +75,6 @@ const calculateZScore = (gender, ageInMonths, weight, height) => {
     let hfaReference = getHfaReference(gender, ageInMonths);
     let wfhReference = getWfhReference(gender, height);
 
-    //console.log(`weight ${weight} wfa ${JSON.stringify(wfaReference)}`);
-    
     return {
         wfa: calculate(weight, wfaReference),
         hfa: calculate(height, hfaReference),
@@ -66,8 +86,6 @@ const zScore = (individual, asOnDate, weight, height) => {
     let ageInMonths = individual.getAgeInMonths(asOnDate);
     let gender = _.get(individual, "gender.name");
 
-    //console.log(`ageInMonths ${ageInMonths} gender ${gender}`);
-
     return calculateZScore(gender, ageInMonths, weight, height);
 };
 
@@ -86,4 +104,4 @@ const projectedSD2NegForWeight = (individual, asOnDate) => {
     return projectedSD2Neg;
 }
 
-export {zScore as default, projectedSD2NegForWeight};
\ No newline at end of file
+export {zScore as default, projectedSD2NegForWeight};
diff --git a/src/test/child/zScoreCalculatorTest.js b/src/test/child/zScoreCalculatorTest.js
index 0cd0130..e1c3ac2 100644
--- a/src/test/child/zScoreCalculatorTest.js
+++ b/src/test/child/zScoreCalculatorTest.js
@@ -5,7 +5,7 @@ import moment from "moment";
 
 describe("zScoreCalculator", () => {
     describe("zScore()", () => {
-        var individual, male, female;
+        let individual, male, female;
 
         beforeEach(() => {
             male = new Gender();
@@ -28,6 +28,9 @@ describe("zScoreCalculator", () => {
             let zScores, today = new Date();
             individual.dateOfBirth = moment(today).subtract(1, 'month');
 
+            zScores = zScore(individual, today, 1.2, 54.7);
+            assert.equal(zScores.wfa, -6.7);
+
             zScores = zScore(individual, today, 4.5, 54.7);
             assert.equal(zScores.wfa, 0);
 
@@ -60,7 +63,7 @@ describe("zScoreCalculator", () => {
             //2 year old girl
             individual.dateOfBirth = moment(today).subtract(24, 'month');
 
-            assert.equal(zScore(individual, today, 8.1, ).wfa, -3);
+            assert.equal(zScore(individual, today, 8.1,).wfa, -3);
             assert.equal(zScore(individual, today, 9).wfa, -2);
             assert.equal(zScore(individual, today, 10.2).wfa, -1);
             assert.equal(zScore(individual, today, 11.5).wfa, 0);
@@ -186,4 +189,4 @@ describe("zScoreCalculator", () => {
             assert.approximately(actual, 6.47, 0.01);
         });
     });
-});
\ No newline at end of file
+});