A taxpayer is any person or entity that is required to pay taxes to a government. In the United States, the term covers a wide range: individual citizens, resident aliens, corporations, partnerships, estates, and trusts. If you earn income, own property, or conduct business in a way that triggers a tax obligation, you are a taxpayer in the eyes of the IRS, whether or not you actually owe money at the end of the year.
Who Counts as a Taxpayer
The IRS classifies taxpayers into two broad groups: United States persons and foreign persons. A U.S. person includes any citizen or resident of the United States, a domestic partnership, a domestic corporation, and most estates and trusts administered under U.S. court supervision. Foreign persons include nonresident alien individuals, foreign corporations, foreign partnerships, and foreign estates or trusts.
The distinction matters because U.S. persons are generally taxed on their worldwide income, no matter where it’s earned. Foreign persons are typically taxed only on income that comes from U.S. sources or is connected to a U.S. trade or business.
Business entities add another layer. Some entities, like certain corporations, are automatically classified for tax purposes. Others get to choose. A business with two or more members can elect to be taxed as either a partnership or a corporation. A single-member entity can choose to be taxed as a corporation or be “disregarded,” meaning its income flows directly onto the owner’s personal return. This flexibility is often called the “check-the-box” system because the entity literally checks a box on an IRS form to declare how it wants to be treated.
How Non-Citizens Become U.S. Taxpayers
You don’t need to be a U.S. citizen to be treated as a U.S. taxpayer. If you hold a green card, you’re automatically a resident for tax purposes. Even without a green card, you can become a U.S. tax resident by spending enough time in the country under what’s called the substantial presence test.
The test works like this: you must be physically present in the U.S. for at least 31 days during the current year and at least 183 days over a three-year period. That three-year count is weighted. Every day in the current year counts fully, each day in the prior year counts as one-third of a day, and each day two years back counts as one-sixth. So if you spent 120 days in the U.S. each year for three years, your weighted total would be 120 + 40 + 20 = 180 days, just under the threshold.
Certain days don’t count toward the test. If you commute to work in the U.S. from Canada or Mexico, those commuting days are excluded. Days spent in transit between two foreign locations, days as a crew member on a foreign vessel, and days when a medical condition prevented you from leaving are also excluded. Students on F, J, M, or Q visas, foreign government officials on A or G visas, teachers on J or Q visas, and professional athletes competing in charitable events are all treated as “exempt individuals” whose days of presence generally don’t count.
Taxpayer Identification Numbers
Every taxpayer needs an identification number so the IRS can track income, deductions, and payments. The type of number you use depends on who (or what) you are.
- Social Security Number (SSN): Issued by the Social Security Administration, this is the standard ID for U.S. citizens and authorized residents. Most individual taxpayers file using their SSN.
- Employer Identification Number (EIN): Sometimes called a federal tax ID number, this identifies businesses, estates, and trusts. If you start a company or hire employees, you’ll need an EIN. Estates and trusts that must file Form 1041 also use one.
- Individual Taxpayer Identification Number (ITIN): A nine-digit number beginning with “9” that’s formatted like an SSN. It’s available to certain nonresident and resident aliens, their spouses, and dependents who can’t get an SSN but still have a U.S. tax filing obligation.
- Adoption Taxpayer Identification Number (ATIN): A temporary number for people in the process of legally adopting a U.S. citizen or resident child who can’t yet get an SSN for that child in time to file.
- Preparer Tax Identification Number (PTIN): Required for anyone who prepares federal tax returns for compensation. If a paid preparer signs your return, their PTIN should appear on it.
When You’re Required to File
Being a taxpayer doesn’t always mean you need to file a return. Whether you must file depends primarily on your gross income, filing status, and age. For the 2025 tax year, a single filer under 65 must file if gross income reaches $15,750 or more. For head of household filers, the threshold is $23,625. Married couples filing jointly have a threshold of $31,500 when both spouses are under 65, rising to $34,700 when both are 65 or older. Married individuals filing separately face a threshold of just $5.
Self-employment triggers its own rule. If you earn more than $400 in net self-employment income from freelance work, gig jobs, or any independent contracting, you must file regardless of your total income. Other situations that require filing include owing special taxes (like the alternative minimum tax), receiving advance premium tax credits for health insurance, or earning wages of $108.28 or more from a church exempt from employer Social Security taxes.
Even if your income falls below the filing threshold, you may still want to file. If your employer withheld federal income tax from your paychecks, filing a return is the only way to get that money back as a refund. The same applies if you qualify for refundable credits like the Earned Income Tax Credit.
Rights Every Taxpayer Has
The IRS recognizes a formal Taxpayer Bill of Rights that applies to every person or entity dealing with the agency. These ten rights shape what you can expect during audits, collections, and routine interactions.
You have the right to be informed, meaning the IRS must provide clear explanations of tax laws, its own procedures, and any decisions it makes about your account. You have the right to quality service, which includes prompt, courteous assistance and the ability to escalate to a supervisor. You have the right to pay no more than the correct amount of tax, and to have payments applied properly.
If you disagree with the IRS, you have the right to challenge its position and be heard, providing additional documentation and receiving a response. Beyond that, you can appeal most IRS decisions through an independent administrative process, and you generally have the right to take your case to court. The right to finality means you’re entitled to know the time limits for both your challenges and the IRS’s ability to audit a given year or collect a debt.
Privacy and confidentiality round out the protections. The IRS must ensure that any inquiry or enforcement action is no more intrusive than necessary, respects due process, and complies with search and seizure protections. Information you provide cannot be disclosed without your authorization or a legal basis, and the IRS must take action against employees or preparers who misuse your data. You also have the right to retain representation, meaning you can hire a tax professional to deal with the IRS on your behalf.