US taxes confuse Americans who grew up with them, so if your first W-4 form looks like a puzzle, that is the form's fault. Three things carry you through the first year: knowing which ID number you need, knowing whether the IRS counts you as a resident, and understanding that the money taken from each paycheck is an estimate you settle up in April.
SSN vs. ITIN
Two nine-digit numbers, constantly confused. If you are authorized to work, you apply for a Social Security number at a Social Security office (Form SS-5, free). If you have a US tax obligation but are not eligible for an SSN — a spouse or dependent on some visas, an investor, a family member who is not authorized to work — you apply for an ITIN.
| SSN | ITIN | |
|---|---|---|
| Issued by | Social Security Administration | IRS |
| Who gets one | Citizens and people authorized to work | Anyone with a federal tax purpose who cannot get an SSN |
| Says anything about immigration status? | No | No |
| Work authorization? | Comes with it, for those eligible | Never |
| Used for | Wages, benefits, credit files, taxes | Tax returns; accepted by many banks and some card issuers |
How to get an ITIN: file Form W-7 together with the tax return that needs it, either by mail, in person at an IRS Taxpayer Assistance Center, or through a Certifying Acceptance Agent who verifies your passport so you do not have to mail it. The IRS says to allow about 7 weeks, or 9 to 11 weeks during tax season or from overseas. ITINs expire if you stop using them, so file with it each year you are required to.
Resident or nonresident — for tax purposes only
Tax residency is a separate test from immigration status. Under the IRS substantial presence test, you are a resident for the year if you were in the US at least 31 days this year and at least 183 days counting all of this year's days, one-third of last year's, and one-sixth of the year before. Green-card holders are residents from day one. Some visa holders — F-1 and J-1 students and scholars during their exempt years, for example — do not count days for a period and stay nonresidents; they also skip FICA taxes while nonresident. IRS Publication 519 has the full test.
| If you are a… | You file | You are taxed on | Standard deduction? |
|---|---|---|---|
| Resident for tax purposes | Form 1040 | Worldwide income | Yes — $15,750 for a single filer for 2025 |
| Nonresident | Form 1040-NR | US-source income | Generally no, unless a tax treaty allows it |
Tax treaties between the US and about 60 countries can exempt certain income — student stipends, teaching pay, a first-years threshold — from US tax or prevent it being taxed twice. Whether one applies to you depends on your country and visa; the IRS treaty tables and a preparer who handles nonresident returns will tell you.
Withholding, the W-4, and the refund
Your employer takes an estimate of your income tax out of every paycheck — withholding — based on the W-4 form you fill in when you start. In April you file a return that compares the year's withholding with the tax you owed. Withheld too much and you get a refund; too little and you pay the difference by April 15. The taxes-101 lesson on withholding shows how to tune the W-4; how income tax works covers the brackets.
Filing without paying a preparer
If your income is $69,000 or less, the IRS VITA program prepares and e-files your return free at community sites; find one with the VITA locator or call 800-906-9887. Many VITA sites have preparers trained in ITIN applications and nonresident returns. Above that income, IRS Free File offers guided software, and a paid preparer who advertises "1040-NR" or "ITIN" experience is the right kind if your situation involves a treaty. Keep every pay stub, W-2 and prior return in one folder; each year gets easier, and a clean filing history is something an immigration application may one day ask to see.