diff --git a/mod/forum/lang/en/forum.php b/mod/forum/lang/en/forum.php
index 1733e64da63..61494bf0dea 100644
--- a/mod/forum/lang/en/forum.php
+++ b/mod/forum/lang/en/forum.php
@@ -52,6 +52,7 @@ $string['blockperioddisabled'] = 'Don\'t block';
 $string['blogforum'] = 'Standard forum displayed in a blog-like format';
 $string['bynameondate'] = 'by {$a->name} - {$a->date}';
 $string['cachedef_forum_is_tracked'] = 'Forum tracking status for user';
+$string['calendardue'] = '{$a} is due';
 $string['cannotadd'] = 'Could not add the discussion for this forum';
 $string['cannotadddiscussion'] = 'Adding discussions to this forum requires group membership.';
 $string['cannotadddiscussionall'] = 'You do not have permission to add a new discussion topic for all participants.';
diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index 361c6e70be4..cdecf8ae582 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -86,6 +86,8 @@ define('FORUM_DISCUSSION_UNPINNED', 0);
 function forum_add_instance($forum, $mform = null) {
     global $CFG, $DB;
 
+    require_once($CFG->dirroot.'/mod/forum/locallib.php');
+
     $forum->timemodified = time();
 
     if (empty($forum->assessed)) {
@@ -127,6 +129,7 @@ function forum_add_instance($forum, $mform = null) {
         }
     }
 
+    forum_update_calendar($forum, $forum->coursemodule);
     forum_grade_item_update($forum);
 
     $completiontimeexpected = !empty($forum->completionexpected) ? $forum->completionexpected : null;
@@ -162,7 +165,9 @@ function forum_instance_created($context, $forum) {
  * @return bool success
  */
 function forum_update_instance($forum, $mform) {
-    global $DB, $OUTPUT, $USER;
+    global $CFG, $DB, $OUTPUT, $USER;
+
+    require_once($CFG->dirroot.'/mod/forum/locallib.php');
 
     $forum->timemodified = time();
     $forum->id           = $forum->instance;
@@ -249,6 +254,7 @@ function forum_update_instance($forum, $mform) {
         }
     }
 
+    forum_update_calendar($forum, $forum->coursemodule);
     forum_grade_item_update($forum);
 
     $completiontimeexpected = !empty($forum->completionexpected) ? $forum->completionexpected : null;
diff --git a/mod/forum/locallib.php b/mod/forum/locallib.php
index 6f57004d28c..ab333a993ae 100644
--- a/mod/forum/locallib.php
+++ b/mod/forum/locallib.php
@@ -1,5 +1,4 @@
 <?php
-
 // This file is part of Moodle - http://moodle.org/
 //
 // Moodle is free software: you can redistribute it and/or modify
@@ -17,8 +16,15 @@
 
 /**
  * Library of functions for forum outside of the core api
+ *
+ * @package   mod_forum
+ * @copyright 1999 onwards Martin Dougiamas  {@link http://moodle.com}
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+// Event types.
+define('FORUM_EVENT_TYPE_DUE', 'due');
+
 require_once($CFG->dirroot . '/mod/forum/lib.php');
 require_once($CFG->libdir . '/portfolio/caller.php');
 
@@ -700,3 +706,50 @@ function mod_forum_get_tagged_posts($tag, $exclusivemode = false, $fromctx = 0,
             $exclusivemode, $fromctx, $ctx, $rec, $page, $totalpages);
     }
 }
+
+/**
+ * Update the calendar entries for this forum activity.
+ *
+ * @param stdClass $forum the row from the database table forum.
+ * @param int $cmid The coursemodule id
+ * @return bool
+ */
+function forum_update_calendar($forum, $cmid) {
+    global $DB, $CFG;
+
+    require_once($CFG->dirroot.'/calendar/lib.php');
+
+    $event = new stdClass();
+
+    if (!empty($forum->duedate)) {
+        $event->name = get_string('calendardue', 'forum', $forum->name);
+        $event->description = format_module_intro('forum', $forum, $cmid);
+        $event->courseid = $forum->course;
+        $event->modulename = 'forum';
+        $event->instance = $forum->id;
+        $event->type = CALENDAR_EVENT_TYPE_ACTION;
+        $event->eventtype = FORUM_EVENT_TYPE_DUE;
+        $event->timestart = $forum->duedate;
+        $event->timesort = $forum->duedate;
+        $event->visible = instance_is_visible('forum', $forum);
+    }
+
+    $event->id = $DB->get_field('event', 'id',
+            array('modulename' => 'forum', 'instance' => $forum->id, 'eventtype' => FORUM_EVENT_TYPE_DUE));
+
+    if ($event->id) {
+        $calendarevent = calendar_event::load($event->id);
+        if (!empty($forum->duedate)) {
+            // Calendar event exists so update it.
+            $calendarevent->update($event);
+        } else {
+            // Calendar event is no longer needed.
+            $calendarevent->delete();
+        }
+    } else if (!empty($forum->duedate)) {
+        // Event doesn't exist so create one.
+        calendar_event::create($event);
+    }
+
+    return true;
+}
\ No newline at end of file
diff --git a/mod/forum/tests/locallib_test.php b/mod/forum/tests/locallib_test.php
new file mode 100644
index 00000000000..4a03a0d1882
--- /dev/null
+++ b/mod/forum/tests/locallib_test.php
@@ -0,0 +1,73 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * File containing the forum module local library function tests.
+ *
+ * @package    mod_forum
+ * @category   test
+ * @copyright  2018 Shamim Rezaie <shamim@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+
+require_once($CFG->dirroot . '/mod/forum/lib.php');
+
+/**
+ * Class mod_forum_locallib_testcase.
+ *
+ * @copyright  2018 Shamim Rezaie <shamim@moodle.com>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class mod_forum_locallib_testcase extends advanced_testcase {
+    public function test_forum_update_calendar() {
+        global $DB;
+
+        $this->resetAfterTest();
+
+        $this->setAdminUser();
+
+        // Create a course.
+        $course = $this->getDataGenerator()->create_course();
+
+        // Create a forum activity.
+        $time = time();
+        $forum = $this->getDataGenerator()->create_module('forum',
+                array(
+                    'course' => $course->id,
+                    'duedate' => $time
+                )
+        );
+
+        // Check that there is now an event in the database.
+        $events = $DB->get_records('event');
+        $this->assertCount(1, $events);
+
+        // Get the event.
+        $event = reset($events);
+
+        // Confirm the event is correct.
+        $this->assertEquals('forum', $event->modulename);
+        $this->assertEquals($forum->id, $event->instance);
+        $this->assertEquals(CALENDAR_EVENT_TYPE_ACTION, $event->type);
+        $this->assertEquals(FORUM_EVENT_TYPE_DUE, $event->eventtype);
+        $this->assertEquals($time, $event->timestart);
+        $this->assertEquals($time, $event->timesort);
+    }
+}
\ No newline at end of file