US Tax System Explained: Federal, State and Filing

The United States runs one of the world's most layered tax systems: tax is levied at three levels — federal, state, and local — and each level sets its own rules, rates, and deadlines. The federal layer is administered by the Internal Revenue Service (IRS), part of the US Department of the Treasury. It collects federal income tax, corporate tax, payroll taxes, estate and gift taxes, and excise taxes. Federal law is the same in every state, but it is only the starting point.

States add their own income and sales taxes

Each of the 50 states runs its own tax system on top of the federal one. Most states levy a personal income tax and a sales tax; a handful levy no personal income tax at all, and a few levy no sales tax. State income tax rates published by the states range from 0% to over 13%, and states define taxable income, deductions, and filing rules differently from the federal code. Two neighbours earning the same salary can face materially different total tax bills purely because they live on different sides of a state line.

Cities and counties add a third layer

Below the state, thousands of cities, counties, school districts, and special districts levy their own taxes — most commonly local sales taxes added on top of the state rate, and local income or wage taxes in some jurisdictions. Property tax, which funds schools and local services across the US, is almost entirely a state-and-local tax; the federal government does not tax real estate directly.

Federal individual income tax is progressive: income is sliced into brackets, and each slice is taxed at a higher marginal rate. There are seven federal brackets, and the top published rate is 37% — check the current IRS figures, because bracket thresholds and rates are adjusted and occasionally re-legislated. Your marginal rate is the rate on your last dollar of income; your effective rate, what you actually pay overall, is lower.

Deductions decide what is actually taxed

Tax is charged on taxable income, not gross pay. The standard deduction — a fixed amount every filer can subtract — is published by the IRS each year and is large enough that many filers do not itemize. Those who do can deduct items such as state and local taxes (subject to a published cap), mortgage interest, and charitable gifts, within limits. Retirement saving through employer plans like 401(k)s is tax-deferred: contributions reduce today's taxable income and grow until withdrawal.

Filing status changes the maths

The US taxes by filing status — single, married filing jointly, married filing separately, and head of household — and each status has its own brackets and standard deduction. Married couples usually, but not always, pay less filing jointly. Capital gains on investments held over a year are taxed at preferential published rates rather than ordinary income rates, which is why how long you hold an asset matters as much as how much it grows.

Since the Tax Cuts and Jobs Act of 2017, the federal corporate income tax has been a flat 21% on C-corporation profits — a well-established published figure, though future legislation could change it. States then add their own corporate income or franchise taxes, commonly in the single digits to low double digits, so a company's combined rate depends on where it operates.

Entity choice is a tax decision

The US lets businesses choose their tax skin. C-corporations pay the 21% entity-level tax, and shareholders pay tax again on dividends — the famous double layer. S-corporations, partnerships, and LLCs are generally pass-through: the business itself pays no income tax, and profits flow to owners' personal returns. This single choice changes everything about how a business is taxed, which is why US founders take entity selection as seriously as the business plan.

International rules for cross-border business

The US taxes domestic corporations on worldwide income but allows credits for foreign taxes paid, and post-2017 rules added minimum taxes on certain foreign earnings of US multinationals (the GILTI regime) and a deduction for foreign-derived intangible income (FDII). The published detail is technical and has been amended since — anyone operating across borders should verify the current provisions rather than rely on summaries.

The United States has no federal value-added tax and no national sales tax — this surprises many newcomers, because most of the world's economies run a VAT. Consumption tax in the US is state and local sales tax, and it works very differently from VAT.

Sales tax is charged once, at the till

Sales tax is typically charged only on the final retail sale to the consumer, at a combined state-plus-local rate that is published by each jurisdiction and commonly falls between 0% and about 10%. Unlike VAT, there is no chain of input credits: a business generally does not charge sales tax on business-to-business purchases of goods for resale, using exemption certificates instead. Services are taxed unevenly — many states tax few services, some tax many — so the same invoice can be taxable in one state and exempt in another.

Nexus: why online sellers care

After the 2018 Supreme Court decision in South Dakota v. Wayfair, states can require out-of-state sellers to collect sales tax once their sales into the state cross published economic thresholds — commonly around $100,000 of sales or 200 transactions, varying by state. An e-commerce business shipping nationwide can therefore face registration and filing duties in dozens of states. This is the closest the US comes to a VAT-style compliance burden, and it catches foreign sellers by surprise.

Income and sales tax dominate conversation, but several other US taxes shape real bills. Payroll taxes are the biggest surprise for employees: Social Security tax of 12.4% applies up to a published annual wage base, and Medicare tax of 2.9% applies to all wages — the cost is split evenly between employer and employee (7.65% each on wages up to the base), while the self-employed pay both halves. Verify the current wage base, which is adjusted annually.

Property, estate and excise taxes

Property tax on real estate is levied locally, commonly around 1% of assessed value per year but varying widely, and it is the main funding source for public schools. The federal estate and gift tax applies only above a very high published lifetime exemption, so it touches few families — but several states impose their own lower estate or inheritance taxes. Federal excise taxes target specific goods: fuel, alcohol, tobacco, air travel, and since recent legislation, certain corporate stock buybacks.

State quirks add up

States layer on their own extras: gross-receipts taxes on business turnover in a few states, franchise taxes for the privilege of incorporating, local wage taxes in cities like New York and Philadelphia, and tourism or hotel taxes that visitors pay without noticing. Anyone comparing the US with a single-rate VAT country should total all three layers before concluding which system is lighter.

There is no separate tax registration for most individuals — filing a return creates the record. Individuals file Form 1040, the annual individual income tax return, normally due 15 April following the tax year, with an automatic extension to 15 October on request (an extension to file is not an extension to pay). Employers report wages on Form W-2 and other payers report on the 1099 series; the IRS receives copies, so returns are cross-checked.

Pay-as-you-go: withholding and estimates

The US runs pay-as-you-earn. Employers withhold income tax from wages, and anyone with significant non-wage income — freelancers, landlords, investors — must pay quarterly estimated tax in April, June, September, and January. Underpaying through the year triggers published underpayment penalties, which is why estimated payments are a discipline, not an option.

Businesses and information returns

C-corporations file Form 1120 (also generally due 15 April for calendar-year filers), partnerships file information return Form 1065, and S-corporations file Form 1120-S. Beyond income tax, US persons with foreign financial accounts face the FBAR report and FATCA disclosures — separate filings with their own deadlines and steep published penalties. The calendar-year convention dominates: most individuals and many businesses use 1 January to 31 December as their tax year.

Newcomers usually ask three things: am I a tax resident, what is taxed, and what did my home country not prepare me for. US tax residency for individuals turns on the substantial presence test — a day-count formula over three years, published by the IRS — or on holding a green card. Resident aliens are taxed like citizens: on worldwide income. Nonresident aliens are generally taxed only on US-source income, with treaty relief available where a treaty exists.

Citizenship-based taxation is the American exception

The United States is nearly alone in taxing its citizens on worldwide income regardless of where they live. An American living in Dubai, London, or Singapore still files a US return every year and reports worldwide income, though the foreign earned income exclusion and foreign tax credit usually reduce or eliminate double tax. Renouncing citizenship to escape this is a formal, costly process with its own exit-tax rules — it is not a casual decision.

Migrants' practical surprises

New migrants are often surprised that tips are taxable income, that state tax can exceed expectations in high-tax states, that health insurance is partly a tax matter (premium credits and HSAs), and that there is no VAT refund at the airport — sales tax paid is simply gone. Anyone moving should get advice before the move, not after: the first partial year, with split residency between two countries, is the most error-prone return most people ever file.

Myth: America has low taxes. Corrected: the federal layer looks moderate, but state income tax, local taxes, property tax, and payroll taxes stack up — a high earner in a high-tax state can face a combined marginal rate that rivals Europe's. Myth: there is no tax on online shopping. Corrected: since the Wayfair decision, most states require large remote sellers to collect sales tax; the tax-free internet checkout is largely history.

Myths about Americans abroad

Myth: moving abroad ends US tax. Corrected: citizens file on worldwide income wherever they live; exclusions and credits soften the blow but the filing duty remains. Myth: the US and every country have a treaty preventing double tax. Corrected: the US treaty network is broad but not universal — always check whether a treaty with your country exists and what it covers, because domestic relief rules differ.

Myths about business

Myth: a Delaware company pays no tax. Corrected: Delaware has no state corporate income tax on companies that do not operate there, but federal tax still applies, and operating in another state triggers that state's tax. Myth: tips and cash income are tax-free. Corrected: all income from whatever source is taxable under the federal code — the IRS says so explicitly, and the penalties for hiding cash income are severe.

Readers of a UAE tax site usually want the comparison, so here it is plainly. The UAE levies no personal income tax and no payroll tax on salaries; the US levies both, at three levels of government. The UAE's corporate tax is 9% above a published threshold; the US federal rate is a flat 21% before state taxes. The UAE runs a 5% federal VAT with input credits; the US runs state and local sales taxes with no credit chain, charged once at the till.

Where the US is simpler than its reputation

Two features favour the US: the standard deduction keeps millions of simple returns genuinely simple, and pass-through entities let small businesses avoid entity-level tax entirely. The IRS also publishes unusually detailed free guidance, and free-file options exist for modest incomes.

Where cross-border friction appears

Americans in the UAE remain US filers — the UAE's zero personal tax does not create US foreign tax credits against salary, because there is no UAE tax to credit, though the foreign earned income exclusion often shelters salary within published limits. UAE businesses hiring Americans or selling into the US should check permanent-establishment and treaty questions early; the UAE–US position on agreements should be verified against current official sources rather than assumed from headlines.

Tax figures move. Brackets, standard deductions, wage bases, state rates, and treaty positions are all published annually, and Congress and state legislatures change them. Before making any decision — moving, investing, hiring, or structuring a business — pull the current figure from the official source: the IRS for federal tax, the relevant state revenue department for state tax, and gov.uk-style official portals for any other country involved.

Build a personal tax calendar

The single most useful habit is a calendar: 15 April for individual returns, quarterly estimated dates, W-2 and 1099 arrival in January, state deadlines that may differ, and FBAR/FATCA dates if you hold foreign accounts. Most US penalties are for lateness, not for getting the maths wrong — the system punishes silence more than error.

When to pay for advice

Pay for professional advice when you cross a border (either direction), when you choose a business entity, when equity compensation is involved, when you hold foreign accounts or assets, and when a notice arrives from the IRS or a state. General guides like this one explain the map; an advisor walks your specific route. Confirm with a qualified advisor where you live before acting on anything here.

US tax life runs on fixed dates, and most penalties punish lateness rather than error. The anchor is 15 April: individual Form 1040 returns for the prior calendar year are due, along with any balance of tax owed. An automatic extension to 15 October is available on request — but it extends only the filing, never the payment. Pay late and interest plus failure-to-pay penalties accrue from April.

Quarterly estimated payments

Anyone with income not covered by withholding — freelancers, landlords, investors — pays estimated tax four times a year: commonly 15 April, 15 June, 15 September, and 15 January. Miss a quarter and the underpayment penalty can apply even if the annual return later shows the right total. Published safe-harbour rules let you avoid penalty by paying set percentages of last year’s or this year’s tax — verify the current safe harbours with the IRS.

Information returns and business dates

Employers and payers send W-2s and 1099s by 31 January, which is why filing before February is guesswork. Calendar-year C-corporations file Form 1120 by 15 April; partnerships and S-corporations file information returns by 15 March. FBAR reports for foreign accounts are due 15 April with an automatic extension to 15 October. State deadlines mostly mirror the federal ones — verify each state, because a few differ.

The habit that saves money

Put every deadline in a calendar with a two-week warning. File on time even when you cannot pay in full — the failure-to-file penalty dwarfs the failure-to-pay penalty. Keep prior-year returns and supporting documents for the published retention period; the IRS generally has three years to audit, longer in specified cases.

Withholding, deduction, credit

Withholding is tax taken from pay before you see it. A deduction reduces the income the tax applies to. A credit reduces the tax itself, dollar for dollar — which is why a $1,000 credit beats a $1,000 deduction for anyone above the lowest bracket.

Marginal vs effective rate

Your marginal rate is the tax on your next dollar of income; your effective rate is total tax divided by total income. Confusing the two is the most common error in tax debates — and in personal decisions like whether extra work is worth it.

Nexus and residency

Nexus is the connection that lets a state tax a business — physical presence or, since the Wayfair decision, enough sales into the state. Residency decides which state taxes your personal income; states define it by domicile, day counts, or both, and two states can both claim you at once.

Pass-through and double taxation

A pass-through entity — partnership, S-corporation, most LLCs — pays no entity-level income tax; profits flow to owners’ returns. A C-corporation pays 21% at the entity level and shareholders pay again on dividends: the classic double layer that makes entity choice the most consequential US tax decision.