If for any reason you don’t have enough time to file a tax return before the deadline, normally April 15 of each year, then at least file for an extension to file your income tax return - Form 4868. It’s a small form and it’s easy to fill out. When filed on time, it automatically extends the deadline by 6 months, until October 15th. If you are U.S. citizen or resident, and at the time of the regular due date of the return, you are out of the country for work or in military service, then you are allowed to file your return and pay any amount due up to 2 months after deadline without an extension.
If you expect to owe any tax amount to IRS, pay an estimated amount with your extension, regardless if you qualify for out of country 2 month extension, otherwise you may get penalty and interest for not filing on time. Overpaying is safer than not. Later when filing the tax return, if it’s determined that you overpaid, the amount becomes your tax refund.
The Form 4846 can be downloaded from IRS’s website: Form 4868 - Application for Automatic Extension of Time To File U.S. Individual Income Tax Return
According to IRS, the deadline to file income tax return can be extended by maximum of 6 months, but they have some exceptions for taxpayers that live out of the country. However, IRS allows to file taxes for several years but here is the catch. If you owe any amount, then prepare to pay interest and penalties from the regular due date of the tax year filed. If you have a refund due, then you’ll get the full refund when filing for up to 4 years late. After that time, refunds not claimed by taxpayers become property of the National Treasury.