United States Tax FAQs & Expert Guidance (2025/2026)

For most US taxpayers, the federal income tax filing deadline is Wednesday, April 15, 2026. If you live in Maine or Massachusetts, state holidays (Patriots' Day and Emancipation Day) typically extend this deadline by one or two business days. If you require additional time to organize your documents, you can submit IRS Form 4868 on or before April 15 to secure an automatic six-month extension until October 15, 2026. However, an extension of time to file is not an extension of time to pay: any estimated tax owed must be remitted by April 15 to avoid failure-to-pay penalties and compounding daily interest under IRC Section 6651.

For tax year 2025, the IRS standard deduction amounts adjusted for inflation are $15,000 for single filers, $30,000 for married couples filing jointly, and $22,500 for heads of household. Taxpayers aged 65 or older or blind receive an additional standard deduction of $1,600 (for married individuals) or $2,000 (for unmarried filers). You should only itemize deductions on Schedule A if your combined qualified deductions—including mortgage interest on up to $750,000 of principal debt, state and local taxes (SALT capped at $10,000), qualifying medical expenses exceeding 7.5% of AGI, and charitable donations—exceed your standard deduction limit.

Yes. The United States is one of only two nations that enforces citizenship-based worldwide taxation. If you are a US citizen or lawful permanent resident (Green Card holder) residing outside the country, you must file an annual Form 1040 if your worldwide gross income exceeds the standard filing threshold. To prevent double taxation, eligible expats can utilize the Foreign Earned Income Exclusion (FEIE, Form 2555), which excludes up to $130,000 (2025 indexed threshold) of foreign earned wages, or claim the Foreign Tax Credit (FTC, Form 1116) dollar-for-dollar against taxes paid to a foreign government. Expats receive an automatic two-month filing extension to June 15.

FICA (Federal Insurance Contributions Act) tax consists of two components: Social Security and Medicare. For employees, the Social Security tax rate is 6.2% on gross earnings up to the annual wage base limit of $176,100 for 2025. Any wages earned above $176,100 are exempt from the 6.2% Social Security levy. The Medicare tax rate is 1.45% on all earnings with no upper income cap. Employers match both contributions equally (6.2% and 1.45%), bringing the total FICA contribution to 15.3%. Self-employed individuals pay the full 15.3% as Self-Employment (SE) tax via Schedule SE, but can deduct the employer-equivalent half (50%) above the line on Form 1040.

Under Section 3101(b) of the Internal Revenue Code, an Additional Medicare Tax of 0.9% applies to wages, compensation, and self-employment income exceeding statutory thresholds: $200,000 for single taxpayers and heads of household, $250,000 for married couples filing jointly, and $125,000 for married taxpayers filing separately. Employers are required to begin withholding this 0.9% once an individual employee's wages surpass $200,000 in a calendar year, regardless of the employee's filing status or spouse's income. Reconciliation is completed on IRS Form 8959.

Under the Tax Cuts and Jobs Act (TCJA), the US federal corporate income tax rate is a flat 21% on taxable income for domestic C-Corporations. C-Corps are separate legal entities that file Form 1120. Profits are subject to corporate tax at 21%, and when distributed as dividends to individual shareholders, they face a second layer of taxation (qualified dividends are taxed at 0%, 15%, or 20%), creating the classic double taxation model. Additionally, corporations must consider state corporate income taxes, which vary from 0% (e.g., Texas, Washington, Wyoming, South Dakota) to over 9% (e.g., California, New Jersey, Minnesota).

LLCs and S-Corporations are pass-through entities for US tax purposes. The entity itself pays no federal corporate income tax. Instead, business profits, losses, credits, and deductions flow directly to the owners' personal tax returns via Schedule K-1. Single-member LLCs are disregarded entities taxed on Schedule C. S-Corporations allow owner-employees to split net profit between a 'reasonable salary' (subject to FICA and payroll withholding) and shareholder distributions (exempt from FICA), generating substantial tax savings while preserving the Section 199A Qualified Business Income (QBI) deduction of up to 20%.

Long-term capital gains apply to profitable assets held for more than one year before sale. For tax year 2025, long-term capital gains rates are 0%, 15%, and 20% based on taxable income thresholds. For single filers, the 0% rate applies up to $48,350; the 15% rate applies from $48,351 to $533,400; and the 20% rate applies to taxable income exceeding $533,400. For married filing jointly, the 0% threshold extends to $96,700, and the 20% rate starts at $600,050. Assets held for one year or less are treated as short-term capital gains and taxed as ordinary income at your highest marginal rate (up to 37%).

The Net Investment Income Tax (NIIT) is a 3.8% surtax levied under Section 1411 of the Internal Revenue Code. It applies to individuals, estates, and trusts that have net investment income (including capital gains, dividends, interest, royalties, and passive rental income) and modified adjusted gross income (MAGI) exceeding statutory thresholds: $200,000 for single filers, $250,000 for married couples filing jointly, and $125,000 for married filing separately. The 3.8% tax applies to the lesser of net investment income or the amount by which MAGI exceeds the threshold.