What is ITIN (Individual Taxpayer Identification Number)?

How it works

The ITIN (Individual Taxpayer Identification Number) is the IRS's tax-only identifier for individuals not eligible for a Social Security Number. A nine-digit number formatted XXX-XX-XXXX, beginning with 9, it identifies the person (not their entity) on every federal personal tax filing.

The ITIN is required when a non-resident must file a US tax return — Form 1040-NR — or claim treaty benefits in a context that requires a US TIN. Common triggers:

• Owning a US LLC that produces ECI (Effectively Connected Income) — Form 1040-NR required.
• Receiving US-source FDAP income and claiming a treaty rate on Form W-8BEN — the treaty section requires a TIN.
• Selling US real estate (FIRPTA withholding triggers a 1040-NR filing).
• Being a non-resident spouse of a US person and electing to file jointly.
• Opening certain US personal financial accounts that require an IRS TIN.

You apply via Form W-7. Three channels with different processing times and friction:

1. With a federal tax return. Attach W-7, the return, and certified passport copies. Mail to the IRS Austin processing center.
2. Through a Certifying Acceptance Agent (CAA). A CAA verifies your passport in person (or via authorised remote process), avoiding the need to mail original documents. Most non-residents go this route.
3. Through an IRS Taxpayer Assistance Center. Limited capacity, US-only locations, requires an appointment.

Processing time is typically 7 to 11 weeks under normal IRS workload, longer during tax season (February–April). The IRS issues the ITIN by mail.

ITIN vs. EIN

The two get confused but solve different problems:

A non-resident founder with a US LLC needs an EIN to operate the LLC. They may also need an ITIN — separately — if the LLC has US-source ECI flowing to them, or if they want to claim treaty rates on a W-8BEN.

Examples

• Mexican founder's US LLC starts producing ECI. The LLC has a US trade or business and the income flows to the founder personally. He must file 1040-NR each year — needs an ITIN. He files W-7 through a CAA in Mexico City; ITIN arrives roughly 8 weeks later; he files his first 1040-NR.
• German investor in US REIT shares. Receives recurring US REIT dividends. He wants the Germany-US treaty rate (15%) instead of the default 30%. The W-8BEN treaty section requires a TIN — he applies for an ITIN under a "treaty benefits" exception (no return required). Once issued, withholding drops from 30% to 15%, applied prospectively.

Common mistakes

• Thinking the LLC needs an ITIN. It doesn't. The LLC needs an EIN. The ITIN is a personal identifier for the owner, separate from anything the entity does.
• Mailing the original passport to the IRS. Allowed but risky — passports can take months to come back. Use a CAA whenever possible to verify identity locally.
• Letting the ITIN expire. Three years of inactivity revokes it. Renewal blocks returns and treaty claims until the new number issues — plan around it.
• Applying without a clear filing requirement. The IRS rejects W-7 applications that don't tie to either a current federal return or one of the listed exceptions (treaty benefits, REIT shares, scholarship, etc.). "I might need it later" is not a valid reason.