The normal due date of April 15 for filing your U.S. Individual Income Tax Return (Form 1040) and paying any tax due is automatically extended to June 15 for Americans resident abroad on April 15. There is no special form to be filed to obtain this extension but you must attach a statement to your return showing that you qualify for the automatic extension. You will owe interest on any tax paid after April 15. However, there are no late filing penalties (the 5% per month or fraction thereof penalty) when an extension of time to file has been obtained to June 15.
If you cannot meet the June 15 extended due date a further extension of time to file your return (but not to pay tax) to October 15 can be obtained by filing Form 4868 prior to June 15. This extension is automatic with filing the Form. Interest is charged from April 15 on any unpaid tax. There is also a late payment penalty of ½ of 1% per month if you have not paid 90% of your tax by June 15, including any tax paid with Form 4868.
To minimize interest and a possible penalty you should make a "best guess estimate" of your unpaid tax and make a payment with your Form 4868, but this is not required to obtain the automatic extension.
If you have recently moved abroad and expect to qualify for the earned income exclusion under either the full calendar year residency test or the 330 day presence test but you have not actually qualified under either test by June 15, the extended due date of your return, you can file Form 2350. This Form must be filed prior to June 15 and requests a further extension of time to file your return until 30 days beyond the ending date of your qualification period. Interest will be charged on unpaid tax when you file your return. Also you may be charged a late payment penalty. Therefore it may be wise to make a tax payment when filing Form 2350.
The Report of Foreign Bank and Financial Accounts is due to be filed on or before June 30. There are no extensions of time for filing this report.
Any due date that falls on a Saturday, Sunday, or legal U.S. holiday is automatically extended to the next business day.