The due date for filing a U.S. federal individual income tax return generally is April 15th. You can receive an automatic 6-month extension of time to file your return if you file an application for automatic extension by the due date of your return.
However, if you are a U.S. citizen or resident living outside of the United States on the due date of your return, you are allowed an automatic 2-month extension until June 15th to file your return and pay any tax due.
Be aware that the deadline for paying tax due to avoid interest is April 15, 2018.