diff --git a/app/lib/__tests__/date-utils.test.ts b/app/lib/__tests__/date-utils.test.ts
new file mode 100644
index 0000000..8b3133d
--- /dev/null
+++ b/app/lib/__tests__/date-utils.test.ts
@@ -0,0 +1,44 @@
+import { describe, it, expect } from "vitest";
+import { localDateTimeToUtcIso } from "../date-utils";
+
+describe("localDateTimeToUtcIso", () => {
+  it("returns null for empty string", () => {
+    expect(localDateTimeToUtcIso("")).toBeNull();
+  });
+
+  it("returns null for null", () => {
+    expect(localDateTimeToUtcIso(null)).toBeNull();
+  });
+
+  it("returns null for undefined", () => {
+    expect(localDateTimeToUtcIso(undefined)).toBeNull();
+  });
+
+  it("returns null for an invalid date string", () => {
+    expect(localDateTimeToUtcIso("not-a-date")).toBeNull();
+  });
+
+  it("converts a valid datetime-local value and round-trips correctly", () => {
+    // The input matches the datetime-local format "YYYY-MM-DDTHH:MM".
+    // Regardless of timezone, the resulting ISO string should parse back
+    // to the same moment in time.
+    const input = "2026-03-11T17:00";
+    const result = localDateTimeToUtcIso(input);
+    expect(result).not.toBeNull();
+    expect(new Date(result!).getTime()).toBe(new Date(input).getTime());
+  });
+
+  it("returns a string ending with 'Z' (UTC designator)", () => {
+    const result = localDateTimeToUtcIso("2026-03-11T10:00");
+    expect(result).not.toBeNull();
+    expect(result!.endsWith("Z")).toBe(true);
+  });
+
+  it("returns a full ISO-8601 string with milliseconds", () => {
+    const result = localDateTimeToUtcIso("2026-06-15T08:30");
+    expect(result).not.toBeNull();
+    // toISOString() always produces "YYYY-MM-DDTHH:MM:SS.mmmZ"
+    expect(result).toMatch(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/);
+  });
+
+});
diff --git a/app/lib/date-utils.ts b/app/lib/date-utils.ts
new file mode 100644
index 0000000..5455009
--- /dev/null
+++ b/app/lib/date-utils.ts
@@ -0,0 +1,24 @@
+/**
+ * Converts a datetime-local input value (local time, no timezone info)
+ * to a UTC ISO string for server submission.
+ *
+ * `datetime-local` inputs use the format "YYYY-MM-DDTHH:MM" and do NOT accept
+ * ISO strings with a timezone designator (e.g. "2026-03-11T17:00:00.000Z").
+ * Setting an ISO UTC string directly on a datetime-local input causes the browser
+ * to silently clear the field value. Use this function with a separate hidden input
+ * to hold the converted UTC value before form submission.
+ *
+ * Returns null when value is empty, nullish, or not a valid date.
+ *
+ * NOTE: The returned ISO string (e.g. "2026-03-11T17:00:00.000Z") is intentionally
+ * incompatible with datetime-local inputs, which only accept "YYYY-MM-DDTHH:MM".
+ * Setting a Z-suffixed string on a datetime-local input causes browsers to silently
+ * clear the field. Always write the result to a separate hidden input, not back to
+ * the datetime-local input itself.
+ */
+export function localDateTimeToUtcIso(value: string | null | undefined): string | null {
+  if (!value) return null;
+  const date = new Date(value);
+  if (isNaN(date.getTime())) return null;
+  return date.toISOString();
+}
diff --git a/app/routes/admin.sports-seasons.$id.events.$eventId.bracket.tsx b/app/routes/admin.sports-seasons.$id.events.$eventId.bracket.tsx
index 613084e..52472fb 100644
--- a/app/routes/admin.sports-seasons.$id.events.$eventId.bracket.tsx
+++ b/app/routes/admin.sports-seasons.$id.events.$eventId.bracket.tsx
@@ -1,5 +1,6 @@
 import { Form, Link } from "react-router";
 import { Fragment, useState, useEffect, useMemo } from "react";
+import { localDateTimeToUtcIso } from "~/lib/date-utils";
 import type { Route } from "./+types/admin.sports-seasons.$id.events.$eventId.bracket";
 
 import { loader, action } from "./admin.sports-seasons.$id.events.$eventId.bracket.server";
@@ -728,13 +729,18 @@ export default function EventBracket({
                                     {/* Add game form */}
                                     <Form method="post" className="flex gap-2 items-end" onSubmit={(e) => {
                                       const form = e.currentTarget;
-                                      const scheduledAtInput = form.elements.namedItem("scheduledAt") as HTMLInputElement;
-                                      if (scheduledAtInput?.value) {
-                                        scheduledAtInput.value = new Date(scheduledAtInput.value).toISOString();
+                                      // Read from the datetime-local display input (not submitted directly)
+                                      const scheduledAtLocal = form.elements.namedItem("scheduledAtLocal") as HTMLInputElement;
+                                      // Write the UTC ISO string into the hidden input that IS submitted
+                                      const scheduledAtHidden = form.elements.namedItem("scheduledAt") as HTMLInputElement;
+                                      if (scheduledAtHidden) {
+                                        scheduledAtHidden.value = localDateTimeToUtcIso(scheduledAtLocal?.value) ?? "";
                                       }
                                     }}>
                                       <input type="hidden" name="intent" value="add-game" />
                                       <input type="hidden" name="matchId" value={match.id} />
+                                      {/* Hidden field holds the UTC ISO string written by onSubmit */}
+                                      <input type="hidden" name="scheduledAt" defaultValue="" />
                                       <div className="flex-1">
                                         <Label className="text-xs">Game #</Label>
                                         <Input
@@ -750,7 +756,7 @@ export default function EventBracket({
                                       <div className="flex-1">
                                         <Label className="text-xs">Date &amp; Time ({localTzAbbr})</Label>
                                         <Input
-                                          name="scheduledAt"
+                                          name="scheduledAtLocal"
                                           type="datetime-local"
                                           className="h-8"
                                         />