U.S. Tax Return Due Date is June 15th (16th for 2013 YR) for Citizens and LPRs Living Outside the U.S.
A basic point in the law that is not well understood is the due date for filing federal income tax returns for USCs and LPRs (where the LPR is a resident, absent a treaty override) residing outside the U.S. Generally both must file IRS Form 1040. See, USCs and LPRs Living Outside the U.S. – Key Tax and BSA Forms
It seems that almost everyone, including many U.S. tax return preparers, erroneously consider April 15th as the due date (for all individual taxpayers), which is only true, if the taxpayer lives in the U.S..
However, if the USC or LPR (where the LPR continues to be an income tax resident; notwithstanding the potential tax treaty override rules) live outside the U.S. the due date of the tax return is June 15th (June 16th in 2014, since the 15th falls on a Sunday). See my earlier post, IRS Beats the Drums – Re: Foreign Assets, Just Days Before April 15,
Finally, both groups of taxpayers (resident or not) can file an automatic extension to file the return on or before October 15th, IRS Form 4868, Application for Automatic Extension of Time To File U.S. Individual Income Tax Return.
It is quite important to file an automatic extension, particularly when any tax may be owing, since the late filing penalty (of up to 25% of the amount of tax owing) can otherwise be applicable.