U.S. taxes: federal, state and local layers explained

1. Why this guide and who it helps

U.S. taxation can feel confusing because it is not a single centralized system. The same income, property, job, investment or business can involve a federal rule, a state return, a local tax, an information filing or a treaty question. This guide is designed as a map: it does not calculate your tax, but it helps you identify which questions must be checked before you act.

It is written for people living in the United States, planning a move, working for a U.S. employer, billing clients as self-employed workers, owning real estate, investing, starting a company or keeping tax ties with France. France-U.S. families need particular care because citizenship, tax residency, source of income, foreign financial accounts and the France-U.S. tax treaty may overlap.

The practical method is to read the relevant chapter, identify the form or agency, and then verify the current official version. Thresholds, brackets, deductions and deadlines change regularly. A strategy that worked for one tax year may be wrong the next year.

2. Federal, state, county and city layers

In the United States, taxes must be analyzed in layers. The federal layer, mainly administered by the IRS, covers income tax, certain payroll taxes, excise taxes, estate and gift taxes, and multiple information returns. This national layer does not replace state obligations.

Each state can apply its own rules: individual income tax, corporate income tax, franchise tax, sales tax, fuel tax, insurance tax, registration fees and employer obligations. Two neighboring states can treat the same wage, retirement income or investment income differently. State residency is therefore as important as federal tax residency in many cases.

Counties, cities and special districts add another layer. They may fund schools, roads, water, emergency services or infrastructure through property tax, hotel occupancy tax, business licenses, wage taxes or special assessments. Before buying, renting, hiring or selling online, check the exact address, not just the state.

3. Federal individual income tax

Federal income tax is generally reported through an annual return. For many individuals, Form 1040 is the central form, with schedules added depending on the types of income and deductions involved. Wages are usually reported on Form W-2, contractor or investment income on various Forms 1099, self-employment activity on Schedule C, and capital gains on the relevant forms and schedules.

The U.S. system distinguishes gross income, adjustments, taxable income, deductions, credits and payments already made. A deduction reduces taxable income, while a credit reduces the tax itself. That difference explains why two households with the same gross income can have very different final liabilities.

Form 1040 is not just a calculation sheet. It summarizes filing status, dependents, worldwide or U.S.-source income depending on status, withholding, estimated payments, credits and sometimes penalties. Every number should be supported by records kept with the taxpayer's files.

4. Withholding: W-4 and payroll

The U.S. system expects employees to prepay part of their tax during the year. Form W-4 gives an employer the information needed to estimate federal withholding: filing status, multiple jobs, dependents, other income, estimated deductions or additional voluntary withholding.

A poorly completed W-4 can create two opposite problems. Too much withholding means the taxpayer advances cash and waits for a refund. Too little withholding can create a large balance due and possibly an underpayment penalty. Life changes should therefore trigger a review: marriage, divorce, child, second job, self-employment income, move to another state or investment income.

A U.S. pay stub often separates federal income tax, Social Security, Medicare, state income tax, local tax and other deductions. It is useful to compare several pay stubs during the year and reconcile them with the year-end Form W-2.

5. FICA: Social Security and Medicare

FICA stands for Federal Insurance Contributions Act. On employee payroll, it mainly covers Social Security, also called OASDI, and Medicare. These payroll taxes are not a prepayment of federal income tax. They fund social programs and appear on separate lines of the pay stub.

Social Security applies up to an annual wage base that changes over time. Medicare follows a different pattern and can continue above that wage base, with an Additional Medicare Tax at certain income levels. The employer also pays its share, which is why the full cost of an employee is higher than gross wages alone.

For someone coming from France, FICA must be separated from federal income tax, state income tax and French social contributions. In some cross-border situations, a totalization agreement or certificate of coverage may become relevant, but that point must be reviewed with the applicable rules and agencies.

6. Self-employed workers and self-employment tax

A self-employed person may not receive a W-2 and may not have an employer withholding tax during the year. Business activity is often reported on Schedule C, separating receipts, ordinary and necessary expenses, net profit and supporting records. Forms 1099 can help reconstruct income, but the absence of a 1099 does not mean the income is not taxable.

Self-employment tax is calculated through Schedule SE. It is broadly similar to Social Security and Medicare payroll taxes, but the self-employed person bears the equivalent of both the employer and employee portions. A deduction may apply for the employer-equivalent share under the rules in force, but that does not remove the cash-flow need.

Quarterly estimated payments are often the weak point for new entrepreneurs. Consultants, drivers, content creators, tradespeople and short-term rental operators may need to plan for federal income tax, self-employment tax, state tax, city obligations, licenses and sometimes sales tax.

7. Alternative Minimum Tax

The Alternative Minimum Tax, or AMT, exists to limit the effect of certain deductions, exclusions or tax preferences. A taxpayer may need to compute tax under the regular rules and then under an alternative calculation. If the AMT result exceeds regular tax, the difference becomes payable.

AMT can arise when income is high, when certain itemized deductions are significant, or when specific items such as incentive stock options enter the calculation. It is not only a topic for extremely wealthy taxpayers. Professional income, equity compensation or investment transactions can bring it into play.

Form 6251 is used to test AMT. Do not judge AMT exposure from gross income alone. The result depends on income composition, family status, tax preferences and the thresholds for the tax year. A projection before exercising stock options or completing a major sale can prevent a surprise.

8. Standard deduction and itemized deductions

After income is determined, the federal system allows the tax base to be reduced either by the standard deduction or by itemized deductions. The standard deduction is a flat amount published for the tax year and varies by filing status. Itemized deductions are listed on Schedule A.

Schedule A may include certain state and local taxes, qualifying mortgage interest, gifts to eligible organizations, medical expenses above a threshold and other tightly defined items. Each line has conditions, limits, exceptions and documentation requirements. A tax paid locally is not automatically deductible federally.

Taxpayers generally choose the more favorable option between the standard deduction and itemized deductions. However, the choice can interact with AMT, state tax, credits or real estate planning. French taxpayers should avoid importing French tax habits into U.S. filings. Similar words may hide very different rules.

9. Corporations, partnerships and common forms

The choice of U.S. legal structure has major tax consequences. A sole proprietorship is usually attached directly to the individual. A partnership or certain LLCs can produce pass-through reporting, with income allocated to owners through Schedule K-1. A C corporation is generally taxed at the corporate level, and dividends may then be taxed to shareholders.

An S corporation adds another layer of complexity. It can avoid some double taxation effects, but it has eligibility rules, shareholder restrictions and reasonable compensation requirements for active owner-employees. This election can be unavailable or risky for some nonresidents or international structures.

An LLC is not one single tax regime. It may be treated as a disregarded entity, partnership, corporation or make a different election depending on forms and facts. France-U.S. entrepreneurs should also review how France sees the entity, withholding, treaty issues and banking information reporting.

10. State income taxes

State income tax is one of the biggest differences between the United States and a centralized system. Some states do not levy individual income tax, but may rely on sales tax, property tax or other taxes. Others apply progressive or flat income tax systems, with their own deductions, credits and dates.

State residency can create disputes. Moving, teleworking, keeping a home in a former state, counting days of presence or operating a business may create obligations in more than one jurisdiction. Source rules also matter: wages earned physically in a state, real estate rented locally or business activity with nexus can require a nonresident return.

Always check the Department of Revenue for the relevant state. Tax software can help, but it cannot decide factual issues such as domicile, days of presence, sourcing and credits for tax paid to another state.

11. Local income or payroll taxes

Beyond the state level, some cities and counties impose taxes on income, wages, business licenses, hotel rooms, short-term rentals or specific activities. A taxpayer may therefore have a federal return, a state return and a separate local obligation.

Employers must be careful when hiring across multiple cities. The employee's work location, residence and employer registration location can trigger different rules. For a small business, missing a business license or local tax can become more expensive than the original amount.

The best method is to start from the exact address: city, county, ZIP code and school district, then check official local websites. Large platforms and marketplaces do not always cover every obligation of the seller or rental operator.

12. Sales and use tax

U.S. sales tax should not be confused with French VAT. There is no general federal VAT. Sales tax is usually a state and sometimes local tax applied to certain sales of goods or services. The rate charged at checkout may combine several layers.

Use tax complements sales tax when an item was not taxed at purchase but is used in a taxable jurisdiction. Consumers often overlook it. Businesses must pay close attention when purchasing equipment from another state or selling online.

With e-commerce, economic nexus has become central. A business with no physical office in a state may still have to collect sales tax if it exceeds sales or transaction thresholds. Exempt products, taxable services and exemption certificates vary widely.

13. Property tax and special assessments

Property tax is one of the most important recurring costs for U.S. property owners. It is often administered by the county or local districts. The calculation starts with an assessed value, which may differ from market value, and then applies rates set by several entities: county, city, school district, water district or others.

Owners should read valuation notices, exemptions, appeal deadlines and payment dates carefully. A purchase can trigger reassessment, and a mortgage escrow payment can hide the real increase until the annual adjustment. Special assessments may fund roads, sewers, flood protection, schools or other infrastructure.

For a French investor, property tax must be built into net yield together with insurance, HOA dues, maintenance, vacancy, property management, federal tax, state tax and possible withholding on certain nonresident income. See also Real Estate in the USA.

14. Excise and sector taxes

Excise taxes are targeted taxes on certain products, services or economic behaviors. They may apply to fuel, alcohol, tobacco, air transportation, heavy trucks, insurance, communications, wagering, environmental products or regulated activities. They can be federal, state or local.

These taxes matter for businesses because they may be reported on specialized forms, with licenses, records and filing periods of their own. A company selling a taxable product may have to collect, calculate and remit tax even if the amount is embedded in the sales price.

Regulated sectors should review tax before launching. Importing, alcohol distribution, transportation, fuel, insurance or short-term rentals can combine sector taxes, sales tax, business licenses and federal obligations.

15. Estate tax and gift tax

The United States has federal estate and gift tax rules. Estate tax relates to wealth transferred at death, while gift tax relates to certain lifetime transfers. Thresholds, annual exclusions, unified credit and carryover rules change with law and tax year.

International families face more complexity. A U.S. citizen, tax resident, nonresident owning U.S.-situs assets, mixed-nationality couple or estate with assets in multiple countries may fall under different rules. U.S.-situs assets must be identified carefully.

Form 706 relates to estates in applicable cases, and Form 709 relates to certain gifts. Wealth planning must coordinate civil law, state succession law, federal tax, tax treaties and French rules. A simple-looking gift can create unexpected reporting duties.

16. Foreign taxpayers, treaties and information returns

International tax is one of the most sensitive areas. A taxpayer may be a U.S. citizen, a tax resident under the substantial presence test, a green card holder, a nonresident with U.S.-source income or a foreign investor. Each status changes the forms, taxable base and withholding rules.

A nonresident often uses Form 1040-NR for relevant U.S. income. But the analysis must also cover effectively connected income, fixed or determinable income, withholding, Forms W-8, real estate income, sale gains and tax treaties. The France-U.S. treaty may allocate taxing rights, but it does not automatically eliminate filing obligations.

Foreign accounts and financial assets add another layer. Form 8938 is tied to FATCA and may be attached to the tax return. FBAR is filed with FinCEN and concerns foreign financial accounts above specific thresholds. Penalties can be significant, so these filings should be treated as priority compliance items, not minor attachments.

17. Calendar, extensions and estimated payments

The U.S. tax calendar is built around a simple idea: tax should be paid during the year through withholding or estimated payments. For calendar-year individuals, Form 1040 is commonly due around April 15 when that date is a business day, but it can shift for weekends, holidays, disaster relief or official announcements.

Form 4868 can extend the federal filing deadline, but it is not a free permission to pay later. The taxpayer should estimate and pay what is due by the payment deadline to limit interest and penalties. States may have their own extension rules.

Self-employed workers, investors, landlords and taxpayers without enough withholding often use Form 1040-ES for estimated payments. Deadlines should be placed on an annual calendar, and payment confirmations should be kept, especially when several jurisdictions are involved.

18. Interest, penalties and audits

U.S. tax penalties can arise from late filing, late payment, underpayment of estimates, rejected payments, missing information returns, negligence, insufficiently supported positions or foreign asset omissions. Interest can run in addition to certain penalties.

Compliance depends heavily on documentation. Keep W-2s, 1099s, bank statements, contracts, invoices, estimated payment proofs, deduction records, mileage logs, real estate closing documents, valuation evidence and agency correspondence. In an audit, the practical task is often to reconstruct and support what was reported.

IRS or state notices should not be ignored. Some are automated and can be resolved with an explanation or proof, but response deadlines matter. An unanswered letter can turn into collection, a tax lien or a banking problem.

19. Forms and systems

U.S. tax forms are an administrative language. Form 1040 summarizes the individual return, but it points to specialized schedules and forms. W-4 acts upstream through payroll. Schedule A lists certain itemized deductions. Schedule C and Schedule SE relate to self-employment. Form 1040-ES is used for estimated payments. Form 4868 requests a filing extension.

Wealth and international obligations use additional tools: Form 706 for certain estates, Form 709 for certain gifts, Form 8938 for specified foreign financial assets, Form 1040-NR for certain nonresidents, and FBAR through FinCEN for foreign financial accounts. EFTPS is used for federal electronic payments, especially for businesses and estimated payments.

20. Annual checklist

Good tax preparation starts before filing season. Taxpayers should organize documents throughout the year, track life changes and note deadlines. Waiting until April to find income records, deductions and estimated payments increases the risk of mistakes.

1. Employee: verify W-2, W-4, address, filing status, state residency, local taxes, refunds, credits and family changes.
2. Household employer: identify domestic employees, wages paid, possible withholding, Schedule H, insurance, state duties and payment proof.
3. Business: maintain books, reconcile 1099s, invoices, payroll, sales tax nexus, licenses, estimated payments, deductible expenses and bank records.
4. International: list foreign accounts, financial assets, French income, withholding, treaty issues, Form 8938, FBAR and exchange-rate support.

22. Frequently asked questions

23. Official links

The links below should take priority over summaries, forums, videos or general articles. Tax law changes by tax year. Always check the date of the page, the form revision, the instructions and the latest IRS releases. For states and cities, also consult local agencies, because the IRS does not cover every local rule.