The Internal Revenue Service requires tax ID numbers for federal income tax purposes. If you already have a Social Security number, it's also your tax ID number. However, alternate taxpayer ID numbers are available for those who don't qualify for a Social Security number. In some cases, you may need a business ID number in addition to a personal tax number.
Basic Filing Requirements
The law requires you to supply a tax ID on all your federal returns and related paperwork. In addition to your own number, you generally must provide a Social Security number or alternate ID number for everyone you claim as a dependent, such as your spouse or children. You do not need a tax ID number for any child who died the year she was born.
Obtaining a Social Security Number
To obtain a Social Security number for yourself or a dependent, you must provide a minimum of two documents proving the applicant's identity, age and U.S. citizenship or legal immigrant status. A noncitizen applicant must normally also show proof of the legal right to work in the U.S. Complete and file the application on the Social Security Administration website to receive a Social Security number.
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Individual Taxpayer Identification Number
Resident and nonresident aliens who can't work in the U.S. can obtain an Individual Taxpayer Identification Number, or ITIN, for tax purposes. The spouse or other dependent of an alien also qualifies for this number. Complete and return Form W-7, available on the IRS website, according to the instructions on the application. You must supply documentation of the applicant's identity and foreign or alien status and in most cases include a federal tax return.
If you are adopting a child, you can obtain a temporary tax ID for him. This is necessary only if you must file federal incomes taxes before the child gets a Social Security number. However, the child must be U.S. citizen or legal resident to qualify for this number, called an Adoption Taxpayer Identification Number, or ATIN. Obtain an ATIN by completing and filing Form W-7A, available on the IRS website.
Your Business Taxes
You may need an additional tax ID for business purposes. The IRS requires an Employer Identification Number, or EIN, to file taxes for a partnership, corporation or any business with employees. An EIN is also required to file taxes for an estate or trust using IRS Form 1041. If you are a paid income tax professional, you need a special number for your clients' returns, a Preparer Tax Identification Number, or PTIN. The IRS website supplies instructions for obtaining an EIN or PTIN.
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