diff --git a/public/js/calculators.js b/public/js/calculators.js
index 06c32b5..0d2815a 100644
--- a/public/js/calculators.js
+++ b/public/js/calculators.js
@@ -2,6 +2,7 @@ import { parseAgeMonths, formatParsedAge } from './calculators/age.js';
 import { calculateAapBilirubinAssessment, classifyBhutaniRisk, loadAapBilirubinThresholds, loadBhutaniZones } from './calculators/bilirubin.js';
 import { calculateBMIAssessment, loadBmiLmsData } from './calculators/bmi.js';
 import { calculateBPAssessment, computeBPPercentile, loadBpReferenceData } from './calculators/bp.js';
+import { calculateBsa, calculateWeightBasedDose } from './calculators/dosing.js';
 import { loadEquipmentData, renderEquipmentResult } from './calculators/equipment.js';
 import { loadGrowthLmsData } from './calculators/growth.js';
 import { initImageLightbox } from './calculators/lightbox.js';
@@ -497,7 +498,7 @@ initImageLightbox();
       var height = parseFloat(document.getElementById('bsa-height').value);
       if (!weight || !height) { showToast('Enter weight and height', 'error'); return; }
 
-      var bsa = Math.sqrt(height * weight / 3600);
+      var bsa = calculateBsa(weight, height);
       var resultDiv = document.getElementById('bsa-result');
       resultDiv.classList.remove('hidden');
       resultDiv.innerHTML =
@@ -527,10 +528,10 @@ initImageLightbox();
 
       if (!weight || !dosePerKg) { showToast('Enter weight and dose', 'error'); return; }
 
-      var singleDose = weight * dosePerKg;
-      var capped = false;
-      if (maxDose > 0 && singleDose > maxDose) { singleDose = maxDose; capped = true; }
-      var dailyDose = singleDose * freq;
+      var dose = calculateWeightBasedDose(weight, dosePerKg, freq, maxDose, conc);
+      var singleDose = dose.singleDose;
+      var dailyDose = dose.dailyDose;
+      var capped = dose.capped;
 
       var rows = '<div class="calc-result-item"><div class="calc-result-label">Single Dose</div><div class="calc-result-value">' + singleDose.toFixed(1) + ' <span style="font-size:12px;">mg</span></div>'
         + (capped ? '<div class="calc-result-sub" style="color:var(--red);">Capped at max ' + maxDose + ' mg</div>' : '') + '</div>'
@@ -538,7 +539,7 @@ initImageLightbox();
         + '<div class="calc-result-sub">' + singleDose.toFixed(1) + ' mg x ' + freq + '/day</div></div>';
 
       if (conc > 0) {
-        var vol = singleDose / conc;
+        var vol = dose.volumeMl;
         rows += '<div class="calc-result-item"><div class="calc-result-label">Volume per Dose</div><div class="calc-result-value">' + vol.toFixed(1) + ' <span style="font-size:12px;">mL</span></div>'
           + '<div class="calc-result-sub">at ' + conc + ' mg/mL</div></div>';
       }
diff --git a/public/js/calculators/dosing.js b/public/js/calculators/dosing.js
new file mode 100644
index 0000000..ce7816c
--- /dev/null
+++ b/public/js/calculators/dosing.js
@@ -0,0 +1,20 @@
+export function calculateBsa(weightKg, heightCm) {
+  return Math.sqrt(heightCm * weightKg / 3600);
+}
+
+export function calculateWeightBasedDose(weightKg, dosePerKg, frequencyPerDay, maxDoseMg, concentrationMgPerMl) {
+  var singleDose = weightKg * dosePerKg;
+  var capped = false;
+  if (maxDoseMg > 0 && singleDose > maxDoseMg) {
+    singleDose = maxDoseMg;
+    capped = true;
+  }
+  var dailyDose = singleDose * frequencyPerDay;
+  var volumeMl = concentrationMgPerMl > 0 ? singleDose / concentrationMgPerMl : null;
+  return {
+    singleDose: singleDose,
+    dailyDose: dailyDose,
+    volumeMl: volumeMl,
+    capped: capped
+  };
+}
diff --git a/test/calculators-data.test.js b/test/calculators-data.test.js
index a6e8bfa..f1ddf39 100644
--- a/test/calculators-data.test.js
+++ b/test/calculators-data.test.js
@@ -402,3 +402,20 @@ test('BP calculator preserves legacy outputs across sex/age/height/BP combinatio
     assert.equal(actual.classification.classification, expected.classification, expected.name + ' classification');
   });
 });
+
+test('dosing helpers preserve BSA and weight-based dose outputs', async () => {
+  const dosing = await import('../public/js/calculators/dosing.js');
+  assert.equal(Number(dosing.calculateBsa(20, 110).toFixed(3)), 0.782);
+
+  const uncapped = dosing.calculateWeightBasedDose(12, 15, 3, 0, 40);
+  assert.equal(uncapped.singleDose, 180);
+  assert.equal(uncapped.dailyDose, 540);
+  assert.equal(uncapped.volumeMl, 4.5);
+  assert.equal(uncapped.capped, false);
+
+  const capped = dosing.calculateWeightBasedDose(40, 15, 4, 500, 50);
+  assert.equal(capped.singleDose, 500);
+  assert.equal(capped.dailyDose, 2000);
+  assert.equal(capped.volumeMl, 10);
+  assert.equal(capped.capped, true);
+});