Many U.S. individuals living abroad are either unaware that they have the same tax filing requirements as those living at home, or believe that they do not need to file a return if their foreign income is below the foreign earned income exclusion amount. All U.S. individuals, regardless of the geographical location or the amount of tax liability (even if no tax is owed), must file a return each year.
U.S. expats who are out of the country are usually given extra 2-month automatic extension to file their tax returns without requesting an extension, which makes the due date June 30th of the following year. However, if there is a balance due, interest will be assessed on it starting after April 15th. There is no penalty for being late if you owe no tax.