diff --git a/src/Dashboard/Widgets/SharpGraphWidgetDataSet.php b/src/Dashboard/Widgets/SharpGraphWidgetDataSet.php
index 154e7f2d8..b73366393 100644
--- a/src/Dashboard/Widgets/SharpGraphWidgetDataSet.php
+++ b/src/Dashboard/Widgets/SharpGraphWidgetDataSet.php
@@ -56,9 +56,10 @@ protected function formatValues(array $values): array
     protected function formatLabels(array $values): array
     {
         if ($this->hasDateLabels) {
-            return array_map(function ($value) {
-                return (new Carbon($value))->setTimezone(config('app.timezone'))->toAtomString();
-            }, array_keys($values));
+            return array_map(
+                fn ($value) => (new Carbon($value))->shiftTimezone('UTC')->toAtomString(),
+                array_keys($values)
+            );
         }
 
         return array_keys($values);
diff --git a/tests/Unit/Dashboard/SharpDashboardTest.php b/tests/Unit/Dashboard/SharpDashboardTest.php
index d506ced64..a7c85d6d5 100644
--- a/tests/Unit/Dashboard/SharpDashboardTest.php
+++ b/tests/Unit/Dashboard/SharpDashboardTest.php
@@ -193,6 +193,7 @@ protected function buildWidgetsData(): void
                     '2026-04-03' => 10,
                     '2026-04-04 12:30:04' => 20,
                     '2026-04-05' => 30,
+                    '2026-04-06 12:30:04+02:00' => 40,
                 ])->setLabel('test')->setColor('blue'));
         }
     };
@@ -203,7 +204,7 @@ protected function buildWidgetsData(): void
                 'key' => 'widget',
                 'datasets' => [
                     [
-                        'data' => [10, 20, 30],
+                        'data' => [10, 20, 30, 40],
                         'label' => 'test',
                         'color' => 'blue',
                     ],
@@ -212,6 +213,7 @@ protected function buildWidgetsData(): void
                     '2026-04-03T00:00:00+00:00',
                     '2026-04-04T12:30:04+00:00',
                     '2026-04-05T00:00:00+00:00',
+                    '2026-04-06T12:30:04+00:00',
                 ],
             ],
         ]);
diff --git a/tests/Unit/Dashboard/Widgets/SharpGraphWidgetDataSetTest.php b/tests/Unit/Dashboard/Widgets/SharpGraphWidgetDataSetTest.php
new file mode 100644
index 000000000..fcc813373
--- /dev/null
+++ b/tests/Unit/Dashboard/Widgets/SharpGraphWidgetDataSetTest.php
@@ -0,0 +1,75 @@
+<?php
+
+use Code16\Sharp\Dashboard\Widgets\SharpGraphWidgetDataSet;
+
+it('formats numeric values as floats', function () {
+    $dataSet = SharpGraphWidgetDataSet::make(['a' => 1, 'b' => 2, 'c' => 3]);
+
+    expect($dataSet->toArray()['data'])->toEqual([1.0, 2.0, 3.0]);
+});
+
+it('formats string numeric values as floats', function () {
+    $dataSet = SharpGraphWidgetDataSet::make(['a' => '1.5', 'b' => '2.7']);
+
+    expect($dataSet->toArray()['data'])->toEqual([1.5, 2.7]);
+});
+
+it('returns array keys as labels by default', function () {
+    $dataSet = SharpGraphWidgetDataSet::make(['foo' => 10, 'bar' => 20]);
+
+    expect($dataSet->toArray()['labels'])->toEqual(['foo', 'bar']);
+});
+
+it('accepts a collection', function () {
+    $dataSet = SharpGraphWidgetDataSet::make(collect(['a' => 1, 'b' => 2]));
+
+    expect($dataSet->toArray()['data'])->toEqual([1.0, 2.0])
+        ->and($dataSet->toArray()['labels'])->toEqual(['a', 'b']);
+});
+
+it('sets a label', function () {
+    $dataSet = SharpGraphWidgetDataSet::make(['a' => 1])
+        ->setLabel('My Dataset');
+
+    expect($dataSet->toArray()['label'])->toEqual('My Dataset');
+});
+
+it('does not include label key when not set', function () {
+    $dataSet = SharpGraphWidgetDataSet::make(['a' => 1]);
+
+    expect($dataSet->toArray())->not->toHaveKey('label');
+});
+
+it('sets a color', function () {
+    $dataSet = SharpGraphWidgetDataSet::make(['a' => 1])
+        ->setColor('#ff0000');
+
+    expect($dataSet->toArray()['color'])->toEqual('#ff0000');
+});
+
+it('does not include color key when not set', function () {
+    $dataSet = SharpGraphWidgetDataSet::make(['a' => 1]);
+
+    expect($dataSet->toArray())->not->toHaveKey('color');
+});
+
+it('formats date labels as UTC atom strings regardless of app timezone', function (string $timezone) {
+    config(['app.timezone' => $timezone]);
+
+    $dataSet = SharpGraphWidgetDataSet::make(['2024-01-15' => 10])->withDateLabels();
+
+    expect($dataSet->toArray()['labels'][0])->toEqual('2024-01-15T00:00:00+00:00');
+})->with([
+    'UTC',
+    'America/New_York', // UTC-5
+    'Asia/Tokyo',       // UTC+9
+]);
+
+it('returns plain keys when withDateLabels is not called', function () {
+    $dataSet = SharpGraphWidgetDataSet::make([
+        '2024-01-15' => 10,
+        '2024-06-01' => 20,
+    ]);
+
+    expect($dataSet->toArray()['labels'])->toEqual(['2024-01-15', '2024-06-01']);
+});