If you're a U.S. citizen or resident alien, the laws on income, estate, gift tax returns, and paying estimated taxes are generally similar whether you're in the United States or abroad. Income you receive anywhere in the world is subject to US income tax regardless of where you live.

When to apply:

If you live outside the United States or are on military service and on assignment outside the United States, you have the right to an automatic extension for two months through June 15 to file for a tax refund. However, if you have tax credits, you must pay them no later than the original refund time on the 15th of April in order to avoid the imposition of interest and late penalties.
If you are unable to file a tax refund on time, you can request an additional extension until October 15th by filling in Form 4868, Form 4868, prior to the due date. However, any payments made after the 15th of June will be subject to interest charges as well as late fines.
Where to apply:
If you are a US citizen or resident alien (green card holder), live in a foreign country, or are a non-resident alien, send your tax refund application to the following mailing address:
Department of the Treasury
Internal Revenue Service Center
Austin, TX 73301-0215
Estimated payments are sent to the following address attached to Form 1040-ES to:
Internal Revenue Service
P.O. Box 660406
Dallas, TX 75266-0406
USA
Taxpayer identification number
Anyone who pays tax when filing for tax returns, or claiming to be a dependent, needs a Social Security Number or Taxpayer Identification Number (ITIN). To get Social Security use Form SS-5, Social Security Card Application. To obtain Form SS-5, or to confirm that you qualify for a Social Security card, you should contact the Social Security Department or visit the Social Security International Operations link. If you or your spouse do not qualify for a Social Security card, you may obtain an ITIN by filling in a Form W-7 with the necessary documentation.
1. The National Income Service is making significant changes to the ITIN under the PATH Act of 2015 of 2015. This means that any identification number that has not been used on tax refunds at least once in three years The latter is considered invalid for tax refund procedures as of January 1, 2017, unless the taxpayer renews it. In addition, all ITINs issued prior to 2013 will begin to lose their validity this year, and taxpayers must renew them.
2. The first numbers issued before 2013 that will lose their validity are the numbers whose middle contains the numbers 78 and 79, (Example: 9XX-79-XXXX). The renewal period for these ITINs began on October 1, 2016. The National Income Service began sending letters to this group of taxpayers in the eighth month (August) informing them of the need to renew their numbers for the purpose of applying for a tax refund, and clarifying the renewal steps for them. The IRS will post an expiry schedule and renew numbers without the numbers 78 and 79 in the middle, at a later time in the future.
3. If taxpayer identification numbers become invalid, and are not renewed before the next year's tax refund filing period, they may face a delay in receiving their refunds, and lose some tax benefits they are entitled to, such as the Child Tax Credit or the US Opportunity Tax Credit (Translator: The privilege belongs to graduate students), until the numbers are renewed. More information is available on the Identification Numbers page on the ITIN page at IRS.gov.
rates:
Amounts appearing on your tax return transaction must be in US dollars. If you received part or all of your income or paid expenses in foreign currency, you must convert the foreign currency into US dollars. The taxpayer often uses the annual exchange rate rates to report the foreign income earned during the year.