diff --git a/app/(main)/evaluations/page.tsx b/app/(main)/evaluations/page.tsx
index 28d4c74..67ce459 100644
--- a/app/(main)/evaluations/page.tsx
+++ b/app/(main)/evaluations/page.tsx
@@ -63,6 +63,7 @@ function SimplifiedEvalContent() {
   );
   const [isEvaluating, setIsEvaluating] = useState(false);
   const [runMode, setRunMode] = useState<RunMode>("batch");
+  const [runDuplicationFactor, setRunDuplicationFactor] = useState<string>("");
   const [nameError, setNameError] = useState<string>("");
   const [submitError, setSubmitError] = useState<string>("");
 
@@ -91,6 +92,15 @@ function SimplifiedEvalContent() {
     else setIsDatasetsLoading(false);
   }, [isAuthenticated, loadStoredDatasets]);
 
+  useEffect(() => {
+    const dataset = storedDatasets.find(
+      (d) => d.dataset_id.toString() === selectedDatasetId,
+    );
+    if (dataset) {
+      setRunDuplicationFactor(String(dataset.duplication_factor));
+    }
+  }, [selectedDatasetId, storedDatasets]);
+
   const handleFileSelect = (event: React.ChangeEvent<HTMLInputElement>) => {
     const file = event.target.files?.[0];
     if (!file) return;
@@ -221,10 +231,32 @@ function SimplifiedEvalContent() {
       return;
     }
 
+    const selectedRunDataset = storedDatasets.find(
+      (d) => d.dataset_id.toString() === selectedDatasetId,
+    );
+
+    const trimmedDuplicationFactor = runDuplicationFactor.trim();
+    let duplicationFactorOverride: number | undefined;
+    if (trimmedDuplicationFactor) {
+      if (!/^[1-9]\d*$/.test(trimmedDuplicationFactor)) {
+        toast.error("Duplication factor must be a whole number of 1 or more");
+        return;
+      }
+      const parsedDuplicationFactor = parseInt(trimmedDuplicationFactor, 10);
+      if (
+        !selectedRunDataset ||
+        parsedDuplicationFactor !== selectedRunDataset.duplication_factor
+      ) {
+        duplicationFactorOverride = parsedDuplicationFactor;
+      }
+    }
+
     setIsEvaluating(true);
     try {
       // `run_mode` is only sent when "fast" — omitting it means the backend
       // defaults to batch, which is the safe behaviour for older clients too.
+      // Likewise, `duplication_factor` is only sent when the user overrides
+      // the dataset's stored value.
       const payload: Record<string, unknown> = {
         dataset_id: parseInt(selectedDatasetId),
         experiment_name: experimentName.trim(),
@@ -232,6 +264,9 @@ function SimplifiedEvalContent() {
         config_version: selectedConfigVersion,
         run_mode: runMode === "fast" ? "fast" : "batch",
       };
+      if (duplicationFactorOverride !== undefined) {
+        payload.duplication_factor = duplicationFactorOverride;
+      }
 
       await apiFetch("/api/evaluations", apiKey, {
         method: "POST",
@@ -244,6 +279,7 @@ function SimplifiedEvalContent() {
       setSelectedConfigId("");
       setSelectedConfigVersion(0);
       setRunMode("batch");
+      setRunDuplicationFactor("");
       toast.success(`Evaluation created!`);
       return true;
     } catch (error: unknown) {
@@ -351,6 +387,8 @@ function SimplifiedEvalContent() {
               setActiveTab={setActiveTab}
               runMode={runMode}
               setRunMode={setRunMode}
+              duplicationFactor={runDuplicationFactor}
+              setDuplicationFactor={setRunDuplicationFactor}
               nameError={nameError}
               submitError={submitError}
             />
diff --git a/app/components/evaluations/EvaluationsTab.tsx b/app/components/evaluations/EvaluationsTab.tsx
index 418277c..4a3f2d1 100644
--- a/app/components/evaluations/EvaluationsTab.tsx
+++ b/app/components/evaluations/EvaluationsTab.tsx
@@ -30,6 +30,8 @@ export interface EvaluationsTabProps {
   setActiveTab: (tab: Tab) => void;
   runMode: RunMode;
   setRunMode: (mode: RunMode) => void;
+  duplicationFactor: string;
+  setDuplicationFactor: (value: string) => void;
   nameError?: string;
   submitError?: string;
 }
@@ -50,6 +52,8 @@ export default function EvaluationsTab({
   setActiveTab,
   runMode,
   setRunMode,
+  duplicationFactor,
+  setDuplicationFactor,
   nameError,
   submitError,
 }: EvaluationsTabProps) {
@@ -160,6 +164,8 @@ export default function EvaluationsTab({
     setActiveTab,
     runMode,
     setRunMode,
+    duplicationFactor,
+    setDuplicationFactor,
     nameError,
     submitError,
   };
diff --git a/app/components/evaluations/RunEvaluationForm.tsx b/app/components/evaluations/RunEvaluationForm.tsx
index 2236378..0e2c2aa 100644
--- a/app/components/evaluations/RunEvaluationForm.tsx
+++ b/app/components/evaluations/RunEvaluationForm.tsx
@@ -30,6 +30,8 @@ interface RunEvaluationFormProps {
   setActiveTab: (tab: Tab) => void;
   runMode: RunMode;
   setRunMode: (mode: RunMode) => void;
+  duplicationFactor: string;
+  setDuplicationFactor: (value: string) => void;
   nameError?: string;
   submitError?: string;
 }
@@ -50,6 +52,8 @@ export default function RunEvaluationForm({
   setActiveTab,
   runMode,
   setRunMode,
+  duplicationFactor,
+  setDuplicationFactor,
   nameError,
   submitError,
 }: RunEvaluationFormProps) {
@@ -140,6 +144,22 @@ export default function RunEvaluationForm({
         </div>
       )}
 
+      {selectedDataset && (
+        <div>
+          <Field
+            label="Duplication Factor (Optional)"
+            type="number"
+            value={duplicationFactor}
+            onChange={setDuplicationFactor}
+            disabled={isEvaluating}
+          />
+          <p className="text-xs mt-1 text-text-secondary">
+            Overrides the dataset&apos;s stored duplication factor for this run
+            only. Defaults to {selectedDataset.duplication_factor}.
+          </p>
+        </div>
+      )}
+
       <div>
         <label className="inline-flex items-center text-xs font-medium mb-1.5 text-text-secondary">
           Run Mode