Getting the space left on the DEFAULT_TABLESPACE of the logged user

SELECT
  ts.tablespace_name,
  TO_CHAR(SUM(NVL(fs.bytes,0))/1024/1024, '99,999,990.99') AS MB_FREE
FROM
  user_free_space fs,
  user_tablespaces ts,
  user_users us
WHERE
  fs.tablespace_name(+)   = ts.tablespace_name
AND ts.tablespace_name(+) = us.default_tablespace
GROUP BY
  ts.tablespace_name;