diff --git a/app/Enums/EventTheme.php b/app/Enums/EventTheme.php
index d851dd9f1f..c910abb344 100644
--- a/app/Enums/EventTheme.php
+++ b/app/Enums/EventTheme.php
@@ -7,6 +7,8 @@
 use App\Dto\ReaderClock;
 use Carbon\CarbonInterface;
 use Illuminate\Http\Request;
+use IntlCalendar;
+use IntlGregorianCalendar;
 
 enum EventTheme: string
 {
@@ -64,7 +66,7 @@ public static function current(?string $choice, CarbonInterface $date): ?self
      */
     public static function choiceFrom(?string $cookie): string
     {
-        if ($cookie === self::DEFAULT || self::tryFrom((string) $cookie) instanceof self) {
+        if ($cookie !== null && ($cookie === self::DEFAULT || self::tryFrom($cookie) instanceof self)) {
             return $cookie;
         }
 
@@ -88,6 +90,16 @@ public static function on(CarbonInterface $date): ?self
 
     private static function readerNow(Request $request): CarbonInterface
     {
-        return now(ReaderClock::of($request)->timeZone);
+        $now = now();
+        $timeZone = ReaderClock::of($request)->timeZone;
+
+        if ($timeZone === null) {
+            return $now;
+        }
+
+        $calendar = new IntlGregorianCalendar($timeZone);
+        $calendar->setTime($now->getTimestampMs());
+
+        return $now->utcOffset(($calendar->get(IntlCalendar::FIELD_ZONE_OFFSET) + $calendar->get(IntlCalendar::FIELD_DST_OFFSET)) / 60000);
     }
 }
diff --git a/composer.json b/composer.json
index a456e10e1d..4b744f53c6 100644
--- a/composer.json
+++ b/composer.json
@@ -10,6 +10,8 @@
     "license": "MIT",
     "require": {
         "php": "^8.5.0",
+        "ext-intl": "*",
+        "lib-icu": ">=57.1",
         "firebase/php-jwt": "^7.2.1",
         "inertiajs/inertia-laravel": "^3.6.0",
         "intervention/image": "^4.4.1",
diff --git a/composer.lock b/composer.lock
index 24587fb3ca..e35b61f2e2 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "ba88d229cb2087c4ed1e7cdcbaae1196",
+    "content-hash": "4b22ff4f9c97c3a0d36fe852ef4006f8",
     "packages": [
         {
             "name": "aws/aws-crt-php",
@@ -15894,7 +15894,9 @@
     "prefer-stable": true,
     "prefer-lowest": false,
     "platform": {
-        "php": "^8.5.0"
+        "php": "^8.5.0",
+        "ext-intl": "*",
+        "lib-icu": ">=57.1"
     },
     "platform-dev": {},
     "plugin-api-version": "2.9.0"
diff --git a/tests/Feature/EventThemeTest.php b/tests/Feature/EventThemeTest.php
index b21ca036ac..c999a1d840 100644
--- a/tests/Feature/EventThemeTest.php
+++ b/tests/Feature/EventThemeTest.php
@@ -36,6 +36,22 @@
         ->assertSee('data-event-theme="halloween"', false);
 });
 
+it('uses browser timezone aliases for the theme and greeting year', function (string $date, string $timeZone, string $theme, int $year): void {
+    Date::setTestNow($date);
+
+    $this->withUnencryptedCookie('time_zone', $timeZone)
+        ->get(route('home'))
+        ->assertOk()
+        ->assertInertia(fn ($page) => $page
+            ->where('eventTheme', $theme)
+            ->where('eventYear', $year));
+})->with([
+    'an eastern alias ahead of UTC' => ['2026-10-28 20:00:00 UTC', 'Asia/Calcutta', 'halloween', 2026],
+    'a western alias during daylight saving time' => ['2026-10-29 04:30:00 UTC', 'US/Eastern', 'halloween', 2026],
+    'a western alias after daylight saving time' => ['2026-11-02 00:30:00 UTC', 'US/Eastern', 'halloween', 2026],
+    'a western alias still in the previous year' => ['2027-01-01 01:00:00 UTC', 'US/Eastern', 'newyear', 2027],
+]);
+
 it('shows the theme the reader picked, whatever the day', function (string $choice): void {
     Date::setTestNow('2026-06-15 12:00:00');
 
@@ -98,8 +114,8 @@
         ->assertOk()
         ->assertInertia(fn ($page) => $page->where('eventYear', $year));
 })->with([
-    'New Year\'s Eve' => ['2026-12-31 23:59:59', 2027],
-    'New Year\'s Day' => ['2027-01-01 00:00:00', 2027],
+    "New Year's Eve" => ['2026-12-31 23:59:59', 2027],
+    "New Year's Day" => ['2027-01-01 00:00:00', 2027],
     'the day after' => ['2027-01-02 12:00:00', 2027],
 ]);
 
diff --git a/tests/Unit/Enums/EventThemeTest.php b/tests/Unit/Enums/EventThemeTest.php
index 5658f0c421..954b1c1737 100644
--- a/tests/Unit/Enums/EventThemeTest.php
+++ b/tests/Unit/Enums/EventThemeTest.php
@@ -19,8 +19,8 @@
     'the day after Christmas' => ['2026-12-26 23:59:59', EventTheme::Christmas],
     'between Christmas and New Year' => ['2026-12-29 23:59:59', null],
     'two days before New Year' => ['2026-12-30 00:00:00', EventTheme::NewYear],
-    'New Year\'s Eve' => ['2026-12-31 12:00:00', EventTheme::NewYear],
-    'New Year\'s Day' => ['2027-01-01 12:00:00', EventTheme::NewYear],
+    "New Year's Eve" => ['2026-12-31 12:00:00', EventTheme::NewYear],
+    "New Year's Day" => ['2027-01-01 12:00:00', EventTheme::NewYear],
     'the day after New Year' => ['2027-01-02 23:59:59', EventTheme::NewYear],
     'after the New Year window' => ['2027-01-03 00:00:00', null],
     'an ordinary day' => ['2026-06-15 12:00:00', null],