Individuals. If you’re a U.S. citizen or resident alien living and working (or on military
duty) outside the United States and Puerto
Rico, file Form 1040 or Form 1040-SR and pay any tax, interest, and penalties due. Otherwise, see April 15, earlier. If you want additional time to file your return, file Form 4868
to obtain 4 additional months to file and pay
what you estimate you owe in tax to avoid
penalties and interest. Then, file Form 1040
or Form 1040-SR by October 15.
However, if you’re a participant in a combat
zone, you may be able to further extend the filing deadline. See Pub. 3, Armed Forces' Tax Guide.