For most taxpayers you can't file your return after April 18 without it being considered late, as April 18 is the deadline to submit your return, pay taxes owed, and file an extension.
The only exception to this is if you're a U.S. citizen or resident alien and you are out of the country on the April 18 deadline.
The IRS considers you out of the country if:
- You're living outside the United States or Puerto Rico and your main place of business or post of duty is outside the United States or Puerto Rico; or
- You're on duty in the military or naval service outside the United States or Puerto Rico