diff --git a/tools/backfill-last-visit-timestamp.sql b/tools/backfill-last-visit-timestamp.sql
new file mode 100644
index 0000000..68b17a9
--- /dev/null
+++ b/tools/backfill-last-visit-timestamp.sql
@@ -0,0 +1,67 @@
+-- Copyright 2016 The Chromium Authors. All Rights Reserved.
+--
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file or at
+-- https://developers.google.com/open-source/licenses/bsd
+
+
+DROP PROCEDURE IF EXISTS BackfillLastVisitTimestamp;
+
+delimiter //
+
+CREATE PROCEDURE BackfillLastVisitTimestamp(
+    IN in_now_ts INT, IN in_days_ago INT, IN in_num_days INT)
+BEGIN
+
+  DECLARE done INT DEFAULT FALSE;
+
+  DECLARE c_user_id INT;
+  DECLARE c_comment_ts INT;
+
+  DECLARE curs CURSOR FOR
+    SELECT MAX(created), commenter_id FROM Comment
+    WHERE created >= in_now_ts - 60 * 60 * 24 * in_days_ago
+    AND   created < in_now_ts - 60 * 60 * 24 * (in_days_ago - in_num_days)
+    GROUP BY commenter_id
+    ORDER BY MAX(created);
+
+  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
+  OPEN curs;
+
+  user_loop: LOOP
+    FETCH curs INTO c_comment_ts, c_user_id;
+    IF done THEN
+      LEAVE user_loop;
+    END IF;
+
+    -- Indicate progress.
+    SELECT c_comment_ts AS 'Processing:';
+
+    -- Set last_visit_timestamp for one user if not already set.
+    UPDATE User
+    SET last_visit_timestamp = IFNULL(last_visit_timestamp, c_comment_ts)
+    WHERE user_id = c_user_id;
+
+  END LOOP;
+
+END;
+
+
+//
+
+
+delimiter ;
+
+
+-- If run locally do all at once:
+-- CALL BackfillLastVisitTimestamp(1476915669, 180, 180);
+
+-- If run on staging or production, consider the last 180 days
+-- in chunks of 30 days at a time:
+-- CALL BackfillLastVisitTimestamp(1476915669,  30, 30);
+-- CALL BackfillLastVisitTimestamp(1476915669,  60, 30);
+-- CALL BackfillLastVisitTimestamp(1476915669,  90, 30);
+-- CALL BackfillLastVisitTimestamp(1476915669, 120, 30);
+-- CALL BackfillLastVisitTimestamp(1476915669, 150, 30);
+-- CALL BackfillLastVisitTimestamp(1476915669, 180, 30);
+