diff --git a/src/Service/Notification/WorkingDayCalculator.php b/src/Service/Notification/WorkingDayCalculator.php
new file mode 100644
index 0000000..314546f
--- /dev/null
+++ b/src/Service/Notification/WorkingDayCalculator.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service\Notification;
+
+use App\Service\PublicHolidayServiceInterface;
+use DateTimeImmutable;
+use Throwable;
+
+final readonly class WorkingDayCalculator
+{
+    public function __construct(
+        private PublicHolidayServiceInterface $holidays,
+    ) {}
+
+    public function isWorkingDay(DateTimeImmutable $date): bool
+    {
+        $dayOfWeek = (int) $date->format('N'); // 1 (lundi) .. 7 (dimanche)
+        if ($dayOfWeek >= 6) {
+            return false;
+        }
+
+        return !$this->isPublicHoliday($date);
+    }
+
+    public function nextWorkingDay(DateTimeImmutable $date): DateTimeImmutable
+    {
+        $candidate = $date->modify('+1 day')->setTime(0, 0, 0);
+        while (!$this->isWorkingDay($candidate)) {
+            $candidate = $candidate->modify('+1 day');
+        }
+
+        return $candidate;
+    }
+
+    private function isPublicHoliday(DateTimeImmutable $date): bool
+    {
+        try {
+            $holidays = $this->holidays->getHolidaysDayByYears('metropole', $date->format('Y'));
+        } catch (Throwable) {
+            return false;
+        }
+
+        return isset($holidays[$date->format('Y-m-d')]);
+    }
+}
diff --git a/tests/Service/Notification/WorkingDayCalculatorTest.php b/tests/Service/Notification/WorkingDayCalculatorTest.php
new file mode 100644
index 0000000..5d98dba
--- /dev/null
+++ b/tests/Service/Notification/WorkingDayCalculatorTest.php
@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Service\Notification;
+
+use App\Service\Notification\WorkingDayCalculator;
+use App\Service\PublicHolidayServiceInterface;
+use DateTimeImmutable;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @internal
+ */
+final class WorkingDayCalculatorTest extends TestCase
+{
+    public function testWeekdayIsWorkingDay(): void
+    {
+        // Mardi 08/07/2025
+        self::assertTrue($this->calculator()->isWorkingDay(new DateTimeImmutable('2025-07-08')));
+    }
+
+    public function testSaturdayAndSundayAreNotWorkingDays(): void
+    {
+        self::assertFalse($this->calculator()->isWorkingDay(new DateTimeImmutable('2025-07-12'))); // samedi
+        self::assertFalse($this->calculator()->isWorkingDay(new DateTimeImmutable('2025-07-13'))); // dimanche
+    }
+
+    public function testPublicHolidayIsNotWorkingDay(): void
+    {
+        self::assertFalse($this->calculator()->isWorkingDay(new DateTimeImmutable('2025-07-14'))); // lundi férié
+    }
+
+    public function testNextWorkingDayFromWeekdayIsTomorrow(): void
+    {
+        // Mardi 08/07 -> Mercredi 09/07
+        self::assertSame(
+            '2025-07-09',
+            $this->calculator()->nextWorkingDay(new DateTimeImmutable('2025-07-08'))->format('Y-m-d')
+        );
+    }
+
+    public function testNextWorkingDayFromFridaySkipsWeekend(): void
+    {
+        // Vendredi 11/07 -> lundi 14/07 est férié -> mardi 15/07
+        self::assertSame(
+            '2025-07-15',
+            $this->calculator()->nextWorkingDay(new DateTimeImmutable('2025-07-11'))->format('Y-m-d')
+        );
+    }
+
+    private function calculator(): WorkingDayCalculator
+    {
+        $holidays = $this->createStub(PublicHolidayServiceInterface::class);
+        $holidays->method('getHolidaysDayByYears')->willReturn([
+            // Lundi 14/07/2025 férié
+            '2025-07-14' => 'Fête nationale',
+        ]);
+
+        return new WorkingDayCalculator($holidays);
+    }
+}