If you are a U.S. citizen or resident alien residing overseas, or are in the military on duty outside the U.S., on the regular due date of your return, you are allowed an automatic 2-month extension to file your return and pay any amount due without requesting an extension.  For a calendar year return, the automatic 2-month extension is to June 15.

If you are unable to file your return by the automatic 2-month extension date, you can request an additional extension to October 15 by filing Form 4868 before the automatic 2-month extension date. However, any tax due payments made after June 15 will be subject to both interest charges and failure to pay penalties.

In general, the tax shown on your return should be paid by the due date of the return, without regard to any extension of time for filing the return.