diff --git a/mod/data/classes/completion/custom_completion.php b/mod/data/classes/completion/custom_completion.php
new file mode 100644
index 00000000000..4ace7a58e50
--- /dev/null
+++ b/mod/data/classes/completion/custom_completion.php
@@ -0,0 +1,72 @@
+<?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/>.
+
+declare(strict_types=1);
+
+namespace mod_data\completion;
+
+use core_completion\activity_custom_completion;
+
+/**
+ * Activity custom completion subclass for the data activity.
+ *
+ * Class for defining mod_data's custom completion rules and fetching the completion statuses
+ * of the custom completion rules for a given data instance and a user.
+ *
+ * @package mod_data
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion extends activity_custom_completion {
+
+    /**
+     * Fetches the completion state for a given completion rule.
+     *
+     * @param string $rule The completion rule.
+     * @return int The completion state.
+     */
+    public function get_state(string $rule): int {
+        global $DB;
+
+        $this->validate_rule($rule);
+
+        $userentries = $DB->count_records('data_records', ['dataid' => $this->cm->instance, 'userid' => $this->userid]);
+        $completionentries = $this->cm->customdata['customcompletionrules']['completionentries'];
+
+        return ($completionentries <= $userentries) ? COMPLETION_COMPLETE : COMPLETION_INCOMPLETE;
+    }
+
+    /**
+     * Fetch the list of custom completion rules that this module defines.
+     *
+     * @return array
+     */
+    public static function get_defined_custom_rules(): array {
+        return ['completionentries'];
+    }
+
+    /**
+     * Returns an associative array of the descriptions of custom completion rules.
+     *
+     * @return array
+     */
+    public function get_custom_rule_descriptions(): array {
+        $entries = $this->cm->customdata['customcompletionrules']['completionentries'] ?? 0;
+        return [
+            'completionentries' => get_string('completiondetail:entries', 'data', $entries),
+        ];
+    }
+}
diff --git a/mod/data/lang/en/data.php b/mod/data/lang/en/data.php
index 23c9822f1cd..4f81b60c09b 100644
--- a/mod/data/lang/en/data.php
+++ b/mod/data/lang/en/data.php
@@ -71,6 +71,7 @@ $string['comments'] = 'Comments';
 $string['commentsaved'] = 'Comment saved';
 $string['commentsn'] = '{$a} comment(s)';
 $string['commentsoff'] = 'Comments feature is not enabled';
+$string['completiondetail:entries'] = 'Make entries: {$a}';
 $string['completionentries'] = 'Require entries';
 $string['completionentriescount'] = 'Count of entries';
 $string['completionentriesdesc'] = 'Minimum number of entries required: {$a}';
diff --git a/mod/data/tests/custom_completion_test.php b/mod/data/tests/custom_completion_test.php
new file mode 100644
index 00000000000..8cd39265c54
--- /dev/null
+++ b/mod/data/tests/custom_completion_test.php
@@ -0,0 +1,216 @@
+<?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/>.
+
+/**
+ * Contains unit tests for core_completion/activity_custom_completion.
+ *
+ * @package   mod_data
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+declare(strict_types=1);
+
+namespace mod_data;
+
+use advanced_testcase;
+use cm_info;
+use coding_exception;
+use mod_data\completion\custom_completion;
+use moodle_exception;
+
+defined('MOODLE_INTERNAL') || die();
+
+global $CFG;
+require_once($CFG->libdir . '/completionlib.php');
+
+/**
+ * Class for unit testing mod_data/activity_custom_completion.
+ *
+ * @package   mod_data
+ * @copyright Simey Lameze <simey@moodle.com>
+ * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class custom_completion_test extends advanced_testcase {
+
+    /**
+     * Data provider for get_state().
+     *
+     * @return array[]
+     */
+    public function get_state_provider(): array {
+        return [
+            'Undefined rule' => [
+                'somenonexistentrule', COMPLETION_DISABLED, 0, null, coding_exception::class
+            ],
+            'Rule not available' => [
+                'completionentries', COMPLETION_DISABLED, 0, null, moodle_exception::class
+            ],
+            'Rule available, user has not created entries' => [
+                'completionentries', COMPLETION_ENABLED, 0, COMPLETION_INCOMPLETE, null
+            ],
+            'Rule available, user has created entries' => [
+                'completionentries', COMPLETION_ENABLED, 2, COMPLETION_COMPLETE, null
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_state().
+     *
+     * @dataProvider get_state_provider
+     * @param string $rule The custom completion rule.
+     * @param int $available Whether this rule is available.
+     * @param int $entries The number of entries.
+     * @param int|null $status Expected status.
+     * @param string|null $exception Expected exception.
+     */
+    public function test_get_state(string $rule, int $available, int $entries, ?int $status, ?string $exception) {
+        global $DB;
+
+        if (!is_null($exception)) {
+            $this->expectException($exception);
+        }
+
+        // Custom completion rule data for cm_info::customdata.
+        $customdataval = [
+            'customcompletionrules' => [
+                $rule => $available
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of the magic getter method when fetching the cm_info object's customdata and instance values.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->will($this->returnValueMap([
+                ['customdata', $customdataval],
+                ['instance', 1],
+            ]));
+
+        // Mock the DB calls.
+        $DB = $this->createMock(get_class($DB));
+        $DB->expects($this->atMost(1))
+            ->method('count_records')
+            ->willReturn($entries);
+
+        $customcompletion = new custom_completion($mockcminfo, 2);
+        $this->assertEquals($status, $customcompletion->get_state($rule));
+    }
+
+    /**
+     * Test for get_defined_custom_rules().
+     */
+    public function test_get_defined_custom_rules() {
+        $rules = custom_completion::get_defined_custom_rules();
+        $this->assertCount(1, $rules);
+        $this->assertEquals('completionentries', reset($rules));
+    }
+
+    /**
+     * Test for get_defined_custom_rule_descriptions().
+     */
+    public function test_get_custom_rule_descriptions() {
+        // Get defined custom rules.
+        $rules = custom_completion::get_defined_custom_rules();
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Instantiate a custom_completion object using the mocked cm_info.
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Get custom rule descriptions.
+        $ruledescriptions = $customcompletion->get_custom_rule_descriptions();
+
+        // Confirm that defined rules and rule descriptions are consistent with each other.
+        $this->assertEquals(count($rules), count($ruledescriptions));
+        foreach ($rules as $rule) {
+            $this->assertArrayHasKey($rule, $ruledescriptions);
+        }
+    }
+
+    /**
+     * Test for is_defined().
+     */
+    public function test_is_defined() {
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+
+        // Rule is defined.
+        $this->assertTrue($customcompletion->is_defined('completionentries'));
+
+        // Undefined rule.
+        $this->assertFalse($customcompletion->is_defined('somerandomrule'));
+    }
+
+    /**
+     * Data provider for test_get_available_custom_rules().
+     *
+     * @return array[]
+     */
+    public function get_available_custom_rules_provider(): array {
+        return [
+            'Completion entries available' => [
+                COMPLETION_ENABLED, ['completionentries']
+            ],
+            'Completion entries not available' => [
+                COMPLETION_DISABLED, []
+            ],
+        ];
+    }
+
+    /**
+     * Test for get_available_custom_rules().
+     *
+     * @dataProvider get_available_custom_rules_provider
+     * @param int $status
+     * @param array $expected
+     */
+    public function test_get_available_custom_rules(int $status, array $expected) {
+        $customdataval = [
+            'customcompletionrules' => [
+                'completionentries' => $status
+            ]
+        ];
+
+        // Build a mock cm_info instance.
+        $mockcminfo = $this->getMockBuilder(cm_info::class)
+            ->disableOriginalConstructor()
+            ->onlyMethods(['__get'])
+            ->getMock();
+
+        // Mock the return of magic getter for the customdata attribute.
+        $mockcminfo->expects($this->any())
+            ->method('__get')
+            ->with('customdata')
+            ->willReturn($customdataval);
+
+        $customcompletion = new custom_completion($mockcminfo, 1);
+        $this->assertEquals($expected, $customcompletion->get_available_custom_rules());
+    }
+}