What federal income tax is
Federal income tax is a progressive levy administered by the Internal Revenue Service (IRS). Rates run from 10% on the lowest income bracket to 37% on the highest. Unlike a flat tax, only the income within each bracket is taxed at that bracket's rate. An employee earning $85,000 does not pay 22% on every dollar, only on the portion of income that falls inside the 22% bracket.
The tax applies to US citizens, US permanent residents, and certain non-resident aliens depending on the source of their income. Employers withhold estimated amounts from each paycheck based on the employee's Form W-4 elections and remit those amounts to the IRS throughout the year.
Core mechanics: brackets, rates, and withholding
Two rates matter when explaining compensation to employees:
- Marginal tax rate - the rate applied to the last dollar of income, which determines the highest bracket reached.
- Effective tax rate - total tax paid divided by total income. Always lower than the marginal rate because lower brackets apply to earlier portions of income.
Withholding tables published by the IRS translate an employee's W-4 information into a dollar amount deducted each pay period. At year-end the employee files a return, reconciles total liability against what was withheld, and either pays the difference or receives a refund.
Key items that reduce taxable income or tax owed:
- Standard deduction - a fixed amount set annually by the IRS, claimed without itemizing individual expenses.
- Itemized deductions - mortgage interest, state and local taxes (capped at $10,000), charitable contributions, and similar items when they exceed the standard deduction.
- Pre-tax benefit contributions - 401(k) deferrals, health savings account contributions, and employer-sponsored health premiums reduce gross income before tax is calculated.
- Tax credits - dollar-for-dollar reductions in tax owed, such as the child tax credit or the earned income tax credit, which are more valuable than equivalent deductions.
Types of taxable income
- Earned income - wages, salaries, tips, bonuses, and self-employment net profit.
- Investment income - dividends, interest, capital gains, and rental income, each with its own rate rules.
- Retirement distributions - withdrawals from traditional 401(k) and IRA accounts, taxed as ordinary income in the year received.
- Other income - alimony from pre-2019 agreements, gambling winnings, certain scholarship amounts, and forgiven debt.
Federal vs. state income tax
Federal income tax applies uniformly across all 50 states. State income tax is an entirely separate obligation that varies by jurisdiction:
| State situation | What employers must handle |
|---|---|
| No state income tax (e.g., Texas, Florida, Wyoming) | Federal withholding only |
| Flat state income tax (e.g., Illinois) | Federal plus a single state rate |
| Progressive state income tax (e.g., California, New York) | Federal plus state brackets, plus sometimes local taxes |
Remote hiring across state lines creates nexus questions: once an employee works from a state, the employer often has payroll tax obligations there. With a distributed US team, the compliance workload multiplies quickly.
Where federal income tax ends and global hiring begins
Federal income tax is a purely domestic framework. The moment a worker is based outside the United States, the rules change entirely, and US federal income tax is often not the primary concern.
US citizens and permanent residents working abroad
US citizens remain subject to federal income tax regardless of where they live. This is unusual globally; most countries tax based on residence, not citizenship. A US software engineer working remotely from Germany still files a US return each year. Employers do not withhold federal income tax for overseas employees unless those employees request it or the employer is a US entity paying a US person.
The Foreign Earned Income Exclusion (FEIE) lets qualifying Americans abroad exclude a portion of their foreign earnings from US taxable income. The figure is adjusted annually. Separately, the Foreign Tax Credit allows a dollar-for-dollar offset against US tax for income taxes paid to another country, reducing double taxation.
Foreign nationals working outside the US
A Brazilian developer hired to work from Brazil owes nothing in US federal income tax on their local salary. They are subject to Brazilian income tax, social contributions, and labor law. US federal tax rules are simply not the relevant framework. The employer's obligation is to withhold and remit under Brazilian rules, not IRS rules.
This is the point most companies stumble on when they first hire internationally. Treating an overseas hire the same way as a US-based employee creates both compliance failures and potential tax authority scrutiny in the worker's home country.
Non-resident aliens doing work in the US
A foreign national who performs services inside the US, even temporarily, may generate US-source income subject to federal income tax or withholding under the Foreign Investment in Real Property Tax Act (FIRPTA) or treaty provisions. Employers paying non-resident aliens for US-performed services often must withhold at a flat 30% rate unless a tax treaty reduces that rate.
How EOR arrangements change the tax picture
When a company uses an Employer of Record to hire workers in another country, the EOR becomes the legal employer in that jurisdiction. The EOR is responsible for:
- Registering as an employer with local tax authorities.
- Withholding the correct local income tax from each payroll cycle.
- Remitting employer-side payroll contributions (social insurance, pension, health funds, and similar obligations that differ by country).
- Issuing local payslips and year-end tax documents in the format required by that country.
US federal income tax withholding does not apply to workers employed through a foreign EOR who are working in that foreign country. The client company is not the employer of record and has no US payroll tax obligation for those workers under this structure.
This distinction matters for payroll reporting. A US company with 20 employees and 10 workers through a Polish EOR does not include the Polish workers on its US payroll tax filings. The EOR handles Polish income tax, ZUS contributions, and local compliance entirely.
Worker classification and the global misclassification risk
One reason global employers care about federal income tax mechanics is the link between tax treatment and worker classification. In the US, misclassifying an employee as an independent contractor means the employer avoided withholding federal income tax, Social Security, and Medicare. The IRS can assess back taxes, penalties, and interest on the employer.
Internationally the stakes are often higher because the tests for employment status differ by country and some carry criminal liability for directors. A few examples:
| Country | Classification test approach | Key risk |
|---|---|---|
| United Kingdom | IR35 rules assess whether the worker would be an employee if hired directly | Client company liable for PAYE and National Insurance if IR35 applies |
| Germany | Multiple-factor test; sole traders working for one client raise automatic suspicion | Back contributions to social insurance funds plus penalties |
| Brazil | Substance over form; courts routinely reclassify contractors | All labor rights owed retroactively including severance and benefits |
| Australia | Multi-factor common law test plus sector-specific rules | Superannuation and withholding tax obligations triggered on reclassification |
| United States | IRS common law test, DOL economic reality test | Back federal income tax withholding, FICA, penalties |
An EOR eliminates the classification ambiguity for those workers by making them employees of record under local law from day one.
Permanent establishment risk and corporate income tax
Federal income tax applies to individuals, but a related risk hits the company itself. When employees or contractors work in a foreign country, their activity can create a permanent establishment for the US parent. If a country's tax authority determines a PE exists, the company may owe corporate income tax in that country on profits attributed to the PE, entirely separate from any individual income tax owed by the worker.
PE risk is one of the main reasons companies use EORs rather than simply letting employees work abroad informally. The EOR structure separates the employment relationship from the client's direct legal presence in the country.
Filing obligations and deadlines
For US domestic payroll, the key employer obligations are:
- Deposit withheld federal income tax and FICA taxes semi-weekly or monthly depending on lookback period tax liability.
- File Form 941 quarterly to reconcile deposits.
- Distribute W-2 forms to employees and file copies with the Social Security Administration by January 31 of the following year.
- Individual tax returns are due April 15. An automatic six-month extension is available by filing Form 4868, but taxes owed are still due by April 15 to avoid interest and penalties.
US citizens abroad get an automatic two-month extension to June 15 (taxes still due by April 15) and can request further extensions. Those claiming the FEIE must also file Form 2555.
Social Security and self-employment tax
Federal income tax is one of several federal levies on earned income. Employers also withhold and match Social Security and Medicare taxes (together called FICA) on US payroll. Self-employed workers pay both halves themselves as self-employment tax, currently at 15.3% on net self-employment income up to the Social Security wage base, then 2.9% for Medicare above that base (plus an additional 0.9% surtax at higher income levels).
For workers employed through foreign EORs, these US FICA taxes do not apply. The equivalent social insurance contributions in the worker's country apply instead, often at rates and caps that differ substantially from US norms.
What changes country to country
Companies expanding globally should expect these differences compared to the US federal income tax model:
- Residence-based vs. citizenship-based taxation - most countries tax residents, not citizens. Moving an employee changes their tax home; for US citizens it does not eliminate the US filing obligation.
- Pay-as-you-earn mechanics - most developed countries use some form of employer withholding, but the thresholds, forms, and remittance schedules vary.
- Employer-side contributions - in many countries the employer's additional cost is far above the US FICA match. French employer social contributions, for example, can add 40-45% on top of gross salary.
- Year-end reconciliation - some countries handle reconciliation automatically through the tax authority; employees never file a personal return. Others require detailed individual filings.
- Tax treaties - the US has bilateral tax treaties with many countries that modify withholding rates, affect PE definitions, and prevent double taxation. Treaty benefits are not automatic; the right forms must be filed.
