diff --git a/cfasim-ui/components/src/NumberInput/NumberInput.md b/cfasim-ui/components/src/NumberInput/NumberInput.md
index 0718672..b48ba29 100644
--- a/cfasim-ui/components/src/NumberInput/NumberInput.md
+++ b/cfasim-ui/components/src/NumberInput/NumberInput.md
@@ -16,6 +16,12 @@ const ageRange = ref([18, 65])
 const coverageRange = ref([0.2, 0.8])
 const minAge = ref(18)
 const maxAge = ref(65)
+const dayMs = 24 * 60 * 60 * 1000
+const dateStart = Date.UTC(2024, 0, 1)
+const dateEnd = Date.UTC(2024, 11, 31)
+const dateRange = ref([Date.UTC(2024, 2, 1), Date.UTC(2024, 8, 30)])
+const formatDate = (ms) =>
+  new Date(ms).toLocaleDateString("en-US", { month: "short", day: "numeric" })
 </script>
 
 <ComponentDemo>
@@ -226,6 +232,51 @@ Range mode works with `percent` and `live` as well:
   </template>
 </ComponentDemo>
 
+### Custom slider display
+
+Pass `slider-display` (a `(value: number) => string` function) to format the
+thumb labels and the min/max labels however you like. The internal model is
+still a number — only the displayed text changes. This applies to single
+sliders and ranges; the regular text input is unaffected.
+
+<ComponentDemo>
+  <div style="width: 300px">
+    <NumberInput
+      v-model:range="dateRange"
+      label="Date range"
+      :min="dateStart"
+      :max="dateEnd"
+      :step="dayMs"
+      :slider-display="formatDate"
+    />
+  </div>
+
+<template #code>
+
+```vue
+<script setup>
+import { ref } from "vue";
+const dayMs = 24 * 60 * 60 * 1000;
+const dateStart = Date.UTC(2024, 0, 1);
+const dateEnd = Date.UTC(2024, 11, 31);
+const dateRange = ref([Date.UTC(2024, 2, 1), Date.UTC(2024, 8, 30)]);
+const formatDate = (ms) =>
+  new Date(ms).toLocaleDateString("en-US", { month: "short", day: "numeric" });
+</script>
+
+<NumberInput
+  v-model:range="dateRange"
+  label="Date range"
+  :min="dateStart"
+  :max="dateEnd"
+  :step="dayMs"
+  :slider-display="formatDate"
+/>
+```
+
+  </template>
+</ComponentDemo>
+
 ### Live slider
 
 With `live`, the model updates while dragging the slider thumb rather than only on release.
diff --git a/cfasim-ui/components/src/NumberInput/NumberInput.test.ts b/cfasim-ui/components/src/NumberInput/NumberInput.test.ts
index 1146fc0..63f711d 100644
--- a/cfasim-ui/components/src/NumberInput/NumberInput.test.ts
+++ b/cfasim-ui/components/src/NumberInput/NumberInput.test.ts
@@ -801,6 +801,33 @@ describe("NumberInput", () => {
     expect((input.element as HTMLInputElement).value).toBe("2.500");
   });
 
+  it("applies sliderDisplay to single-slider thumb and labels", () => {
+    const wrapper = mount(NumberInput, {
+      props: {
+        modelValue: 50,
+        slider: true,
+        min: 0,
+        max: 100,
+        sliderDisplay: (v: number) => `${v} days`,
+      },
+    });
+    expect(wrapper.find(".slider-current").text()).toBe("50 days");
+    const labels = wrapper.findAll(".slider-labels span");
+    expect(labels[0].text()).toBe("0 days");
+    expect(labels[1].text()).toBe("100 days");
+  });
+
+  it("ignores sliderDisplay for regular (non-slider) inputs", () => {
+    const wrapper = mount(NumberInput, {
+      props: {
+        modelValue: 50,
+        sliderDisplay: (v: number) => `${v} days`,
+      },
+    });
+    const input = wrapper.find("input");
+    expect((input.element as HTMLInputElement).value).toBe("50");
+  });
+
   it("syncs local value when model changes externally", async () => {
     const wrapper = mount(NumberInput, {
       props: {
@@ -946,6 +973,27 @@ describe("NumberInput", () => {
       expect(slider.props("modelValue")).toEqual([10, 90]);
     });
 
+    it("uses sliderDisplay to format thumb labels and min/max labels", () => {
+      const fmt = (v: number) => new Date(v).toISOString().slice(0, 10);
+      const start = Date.UTC(2024, 0, 1);
+      const mid = Date.UTC(2024, 5, 1);
+      const end = Date.UTC(2024, 11, 31);
+      const wrapper = mount(NumberInput, {
+        props: {
+          range: [mid, end] as NumberRange,
+          min: start,
+          max: end,
+          sliderDisplay: fmt,
+        },
+      });
+      const thumbs = wrapper.findAll(".slider-thumb");
+      expect(thumbs[0].text()).toBe("2024-06-01");
+      expect(thumbs[1].text()).toBe("2024-12-31");
+      const labels = wrapper.findAll(".slider-labels span");
+      expect(labels[0].text()).toBe("2024-01-01");
+      expect(labels[1].text()).toBe("2024-12-31");
+    });
+
     it("syncs slider when range model changes externally", async () => {
       const wrapper = mount(NumberInput, {
         props: {
diff --git a/cfasim-ui/components/src/NumberInput/NumberInput.vue b/cfasim-ui/components/src/NumberInput/NumberInput.vue
index 68a3897..65aedcb 100644
--- a/cfasim-ui/components/src/NumberInput/NumberInput.vue
+++ b/cfasim-ui/components/src/NumberInput/NumberInput.vue
@@ -29,6 +29,10 @@ const props = defineProps<{
   numberType?: "integer" | "float";
   required?: boolean;
   decimals?: number;
+  // Custom formatter for slider thumb labels and min/max labels. Overrides
+  // the default percent/decimal formatting when provided. Only consulted in
+  // slider/range mode — the text input keeps its own number-shaped formatting.
+  sliderDisplay?: (value: number) => string;
 }>();
 
 function isRangeValue(v: unknown): v is NumberRange {
@@ -109,6 +113,7 @@ function roundToDecimals(v: number, d: number): number {
 
 function formatSliderValue(v: number | undefined) {
   if (v == null) return "";
+  if (props.sliderDisplay) return props.sliderDisplay(v);
   const d = displayDecimals.value;
   if (props.percent) return (v * 100).toFixed(d) + "%";
   return v.toLocaleString("en-US", {