diff --git a/src/wp-includes/comment.php b/src/wp-includes/comment.php
index 0f102d1ea80ee..178528926d909 100644
--- a/src/wp-includes/comment.php
+++ b/src/wp-includes/comment.php
@@ -2875,7 +2875,87 @@ function wp_update_comment_count_now( $post_id ) {
 	$new = apply_filters( 'pre_wp_update_comment_count_now', null, $old, $post_id );
 
 	if ( is_null( $new ) ) {
-		$new = (int) $wpdb->get_var( $wpdb->prepare( "SELECT COUNT(*) FROM $wpdb->comments WHERE comment_post_ID = %d AND comment_approved = '1' AND comment_type != 'note'", $post_id ) );
+		$comments       = (array) $wpdb->get_results( $wpdb->prepare( "SELECT comment_ID, comment_parent, comment_approved FROM $wpdb->comments WHERE comment_post_ID = %d AND comment_type != 'note'", $post_id ) );
+		$comments_by_id = array();
+
+		// Create a lookup array by comment ID.
+		foreach ( $comments as $comment ) {
+			$comments_by_id[ $comment->comment_ID ] = $comment;
+		}
+
+		$comment_count           = 0;
+		$ancestor_approval_cache = array();
+
+		foreach ( $comments as $comment ) {
+			if ( '1' !== $comment->comment_approved ) {
+				$ancestor_approval_cache[ (int) $comment->comment_ID ] = false;
+			}
+		}
+
+		foreach ( $comments as $comment ) {
+
+			if ( '1' !== $comment->comment_approved ) {
+				continue;
+			}
+
+			$comment_id = (int) $comment->comment_ID;
+
+			// Use cached result if this comment's ancestry was already resolved.
+			if ( isset( $ancestor_approval_cache[ $comment_id ] ) ) {
+				if ( $ancestor_approval_cache[ $comment_id ] ) {
+					++$comment_count;
+				}
+				continue;
+			}
+
+			// Walk the ancestor chain, collecting IDs to memoize afterwards.
+			$chain          = array( $comment_id );
+			$visited        = array(
+				$comment_id => true,
+			);
+			$parent_id      = (int) $comment->comment_parent;
+			$has_unapproved = false;
+
+			while ( 0 !== $parent_id ) {
+				if ( isset( $visited[ $parent_id ] ) ) {
+					$has_unapproved = true;
+					break;
+				}
+
+				if ( isset( $ancestor_approval_cache[ $parent_id ] ) ) {
+					if ( ! $ancestor_approval_cache[ $parent_id ] ) {
+						$has_unapproved = true;
+					}
+					break;
+				}
+
+				if ( ! isset( $comments_by_id[ $parent_id ] ) ) {
+					$has_unapproved = true;
+					break;
+				}
+
+				$parent_comment = $comments_by_id[ $parent_id ];
+
+				if ( '1' !== $parent_comment->comment_approved ) {
+					$has_unapproved = true;
+					break;
+				}
+
+				$visited[ $parent_id ] = true;
+				$chain[]               = $parent_id;
+				$parent_id             = (int) $parent_comment->comment_parent;
+			}
+
+			foreach ( $chain as $chain_id ) {
+				$ancestor_approval_cache[ $chain_id ] = ! $has_unapproved;
+			}
+
+			if ( ! $has_unapproved ) {
+				++$comment_count;
+			}
+		}
+
+		$new = $comment_count;
 	} else {
 		$new = (int) $new;
 	}
diff --git a/tests/phpunit/tests/comment/wpUpdateCommentCountNow.php b/tests/phpunit/tests/comment/wpUpdateCommentCountNow.php
index 9dbb1f244ccf8..09fde6c37f06b 100644
--- a/tests/phpunit/tests/comment/wpUpdateCommentCountNow.php
+++ b/tests/phpunit/tests/comment/wpUpdateCommentCountNow.php
@@ -86,4 +86,126 @@ public function test_only_approved_regular_comments_are_counted() {
 	public function _return_100() {
 		return 100;
 	}
+
+	/**
+	 * Test case where a trashed parent comment causes its child comments to be excluded from the comment count.
+	 *
+	 * @ticket 36409
+	 */
+	public function test_trashed_parent_comment_excludes_child_comments_from_count() {
+		$post_id = self::factory()->post->create();
+
+		// Create 2 top-level comments, 2 child comments for the first top-level comment, and a grandchild of that first comment.
+		$parent_comment_id = self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		$child_comment_id = self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_parent'   => $parent_comment_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_parent'   => $parent_comment_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_parent'   => $child_comment_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		$this->assertTrue( wp_update_comment_count_now( $post_id ) );
+		$this->assertSame( '5', get_comments_number( $post_id ) );
+
+		wp_update_comment(
+			array(
+				'comment_ID'       => $parent_comment_id,
+				'comment_approved' => 'trash',
+			)
+		);
+
+		$this->assertTrue( wp_update_comment_count_now( $post_id ) );
+		$this->assertSame( '1', get_comments_number( $post_id ) );
+	}
+
+	/**
+	 * Test case where an unapproved parent comment causes its child comments to be excluded from the comment count.
+	 *
+	 * @ticket 36409
+	 */
+	public function test_unapproved_parent_comment_excludes_child_comments_from_count() {
+		$post_id = self::factory()->post->create();
+
+		// Create 2 top-level comments, 2 child comments for the first top-level comment, and a grandchild of that first comment.
+		$parent_comment_id = self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		$child_comment_id = self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_parent'   => $parent_comment_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_parent'   => $parent_comment_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_id,
+				'comment_parent'   => $child_comment_id,
+				'comment_approved' => 1,
+			)
+		);
+
+		$this->assertTrue( wp_update_comment_count_now( $post_id ) );
+		$this->assertSame( '5', get_comments_number( $post_id ) );
+
+		wp_update_comment(
+			array(
+				'comment_ID'       => $parent_comment_id,
+				'comment_approved' => '0',
+			)
+		);
+
+		$this->assertTrue( wp_update_comment_count_now( $post_id ) );
+		$this->assertSame( '1', get_comments_number( $post_id ) );
+	}
 }