As a US citizen, your Federal Tax Return is due to be filed by April 15 2019, with any tax that is unpaid after this date attracting both interest and potential penalties.
However, American nationals and Green Card holders who are living abroad, are entitled to automatically extend the payment deadline by two months, so that settlement of the tax account becomes due on June 15th 2019.
A further extension (Form 4868) is then available to take the filing deadline up to October 15 2019, but the request for this extension is required to be filed by June 15 2019 latest. For qualifying taxpayers living outside of the US, one final extension is available to December 15, 2019, and should be filed with the Internal Revenue Service in the form of a letter outlining the reasons for the further extension. This request is then granted at the discretion of the IRS.
For Non-Resident Aliens who have a requirement to file a US Federal Return because of effectively connected income as an example, the due date for filing is April 15, 2019. If the Return cannot be filed by that date, Form 4868 must be filed by April 15, 2019. As with regular taxpayers, any taxes owed and unpaid by April 15 will be liable to interest and possible penalties
In addition to Federal tax, many US citizens will for any number of reasons be liable for State income tax with each State having the authority to impose their own system to recover this. So, although filing a Federal tax extension is relatively simple, the differing State rules and conditions can make this process more complex and attention should always be paid to the individual regulations for your home state, or that State where you may have received income from.
Extensions may not be applicable for some. Many taxpayers are keen to submit their tax returns early in order to receive expected refunds. The IRS statistics suggest that 90% of refunds are made to taxpayers within 21 days of submission, although for foreign based taxpayers this is likely to be longer given the more complex nature of their income, deductions and credits.
The IRS officially announces in early January the date when they will be able to accept the submission of Returns and process them accordingly. Tax professionals are in broad agreement that realistically taxpayers should look to file their Returns no earlier than February in order to make that claim for a refund, or pay that tax due.