diff --git a/src/Service/RecurrenceCalculator.php b/src/Service/RecurrenceCalculator.php
new file mode 100644
index 0000000..f501a0b
--- /dev/null
+++ b/src/Service/RecurrenceCalculator.php
@@ -0,0 +1,250 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service;
+
+use App\Entity\Task;
+use App\Entity\TaskRecurrence;
+use App\Enum\RecurrenceType;
+use DateTimeImmutable;
+
+final class RecurrenceCalculator
+{
+    public function getNextDate(Task $task): ?DateTimeImmutable
+    {
+        $recurrence     = $task->getRecurrence();
+        $scheduledStart = $task->getScheduledStart();
+
+        if (null === $recurrence || null === $scheduledStart) {
+            return null;
+        }
+
+        if ($this->hasReachedEnd($recurrence)) {
+            return null;
+        }
+
+        $type     = $recurrence->getType();
+        $interval = $recurrence->getInterval();
+
+        return match ($type) {
+            RecurrenceType::Daily   => $this->nextDaily($scheduledStart, $interval),
+            RecurrenceType::Weekly  => $this->nextWeekly($scheduledStart, $interval, $recurrence->getDaysOfWeek() ?? []),
+            RecurrenceType::Monthly => $this->nextMonthly($scheduledStart, $interval, $recurrence),
+            RecurrenceType::Yearly  => $this->nextYearly($scheduledStart, $interval),
+            default                 => null,
+        };
+    }
+
+    public function getNextEnd(Task $task, DateTimeImmutable $nextStart): ?DateTimeImmutable
+    {
+        $scheduledStart = $task->getScheduledStart();
+        $scheduledEnd   = $task->getScheduledEnd();
+
+        if (null === $scheduledEnd || null === $scheduledStart) {
+            return null;
+        }
+
+        $duration = $scheduledStart->diff($scheduledEnd);
+
+        return $nextStart->add($duration);
+    }
+
+    public function getNextDeadline(Task $task, DateTimeImmutable $nextStart): ?DateTimeImmutable
+    {
+        $scheduledStart = $task->getScheduledStart();
+        $deadline       = $task->getDeadline();
+
+        if (null === $deadline || null === $scheduledStart) {
+            return null;
+        }
+
+        $offset = $scheduledStart->diff($deadline);
+
+        return $nextStart->add($offset);
+    }
+
+    public function hasReachedEnd(TaskRecurrence $recurrence): bool
+    {
+        $maxOccurrences = $recurrence->getMaxOccurrences();
+
+        if (null !== $maxOccurrences && $recurrence->getOccurrenceCount() >= $maxOccurrences) {
+            return true;
+        }
+
+        $endDate = $recurrence->getEndDate();
+
+        if (null !== $endDate) {
+            $today = new DateTimeImmutable('today');
+
+            if ($endDate < $today) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private function nextDaily(DateTimeImmutable $start, int $interval): DateTimeImmutable
+    {
+        return $start->modify(sprintf('+%d days', $interval));
+    }
+
+    private function nextWeekly(DateTimeImmutable $start, int $interval, array $daysOfWeek): DateTimeImmutable
+    {
+        $candidate = $start->modify(sprintf('+%d weeks', $interval));
+
+        if ([] === $daysOfWeek) {
+            return $candidate;
+        }
+
+        $dayNumberMap = $this->getDayNumberMap();
+
+        // Collect target day numbers
+        $targetDayNumbers = [];
+        foreach ($daysOfWeek as $day) {
+            if (isset($dayNumberMap[$day])) {
+                $targetDayNumbers[] = $dayNumberMap[$day];
+            }
+        }
+
+        if ([] === $targetDayNumbers) {
+            return $candidate;
+        }
+
+        sort($targetDayNumbers);
+
+        // Find the first matching day in the week starting from candidate
+        $weekStart       = (int) $candidate->format('N'); // 1=Mon, 7=Sun
+        $candidateDayNum = $weekStart;
+
+        foreach ($targetDayNumbers as $targetDay) {
+            if ($targetDay >= $candidateDayNum) {
+                $diff = $targetDay - $candidateDayNum;
+
+                return $candidate->modify(sprintf('+%d days', $diff));
+            }
+        }
+
+        // Wrap to next week's first matching day
+        $diff = 7 - $candidateDayNum + $targetDayNumbers[0];
+
+        return $candidate->modify(sprintf('+%d days', $diff));
+    }
+
+    private function nextMonthly(DateTimeImmutable $start, int $interval, TaskRecurrence $recurrence): DateTimeImmutable
+    {
+        $dayOfMonth  = $recurrence->getDayOfMonth();
+        $weekOfMonth = $recurrence->getWeekOfMonth();
+        $daysOfWeek  = $recurrence->getDaysOfWeek() ?? [];
+
+        if (null !== $dayOfMonth) {
+            return $this->nextMonthlyByDayOfMonth($start, $interval, $dayOfMonth);
+        }
+
+        if (null !== $weekOfMonth && [] !== $daysOfWeek) {
+            return $this->nextMonthlyByWeekOfMonth($start, $interval, $weekOfMonth, $daysOfWeek[0]);
+        }
+
+        // Fallback: same day of month, interval months ahead
+        return $this->nextMonthlyByDayOfMonth($start, $interval, (int) $start->format('j'));
+    }
+
+    private function nextMonthlyByDayOfMonth(DateTimeImmutable $start, int $interval, int $dayOfMonth): DateTimeImmutable
+    {
+        $year  = (int) $start->format('Y');
+        $month = (int) $start->format('n');
+
+        $month += $interval;
+
+        while ($month > 12) {
+            $month -= 12;
+            ++$year;
+        }
+
+        // Handle month overflow (e.g. dayOfMonth=31 in a 30-day month)
+        $daysInMonth = (int) new DateTimeImmutable(sprintf('%d-%02d-01', $year, $month))->format('t');
+        $day         = min($dayOfMonth, $daysInMonth);
+
+        return new DateTimeImmutable(sprintf(
+            '%d-%02d-%02d %s',
+            $year,
+            $month,
+            $day,
+            $start->format('H:i:s'),
+        ));
+    }
+
+    private function nextMonthlyByWeekOfMonth(DateTimeImmutable $start, int $interval, int $weekOfMonth, string $dayName): DateTimeImmutable
+    {
+        $year  = (int) $start->format('Y');
+        $month = (int) $start->format('n');
+
+        $month += $interval;
+
+        while ($month > 12) {
+            $month -= 12;
+            ++$year;
+        }
+
+        $dayNumberMap = $this->getDayNumberMap();
+        $targetDayNum = $dayNumberMap[$dayName] ?? 1;
+
+        // Find the Nth occurrence of the target weekday in the target month
+        $firstOfMonth = new DateTimeImmutable(sprintf('%d-%02d-01', $year, $month));
+        $firstDayNum  = (int) $firstOfMonth->format('N'); // 1=Mon, 7=Sun
+
+        // Days until first occurrence of target weekday
+        $daysToFirst = ($targetDayNum - $firstDayNum + 7) % 7;
+        $dayOfMonth  = 1 + $daysToFirst + ($weekOfMonth - 1) * 7;
+
+        // Handle overflow (e.g. 5th occurrence that doesn't exist)
+        $daysInMonth = (int) $firstOfMonth->format('t');
+
+        if ($dayOfMonth > $daysInMonth) {
+            // Fall back to last occurrence
+            $dayOfMonth -= 7;
+        }
+
+        return new DateTimeImmutable(sprintf(
+            '%d-%02d-%02d %s',
+            $year,
+            $month,
+            $dayOfMonth,
+            $start->format('H:i:s'),
+        ));
+    }
+
+    private function nextYearly(DateTimeImmutable $start, int $interval): DateTimeImmutable
+    {
+        $year  = (int) $start->format('Y') + $interval;
+        $month = (int) $start->format('n');
+        $day   = (int) $start->format('j');
+
+        // Handle leap year: Feb 29 → Feb 28
+        $daysInMonth = (int) new DateTimeImmutable(sprintf('%d-%02d-01', $year, $month))->format('t');
+        $day         = min($day, $daysInMonth);
+
+        return new DateTimeImmutable(sprintf(
+            '%d-%02d-%02d %s',
+            $year,
+            $month,
+            $day,
+            $start->format('H:i:s'),
+        ));
+    }
+
+    /** @return array<string, int> */
+    private function getDayNumberMap(): array
+    {
+        return [
+            'monday'    => 1,
+            'tuesday'   => 2,
+            'wednesday' => 3,
+            'thursday'  => 4,
+            'friday'    => 5,
+            'saturday'  => 6,
+            'sunday'    => 7,
+        ];
+    }
+}