The federal tax is on the employer, it is an excise tax rather than a withholding, and the rate everyone quotes is not the rate in the statute. Internal Revenue Code section 3301 imposes "on every employer ... an excise tax, with respect to having individuals in his employ, equal to 6 percent of the total wages ... paid by such employer during the calendar year with respect to employment." Section 3306(b)(1) limits the wage base to the first $7,000 paid to an individual in a calendar year, a figure fixed in statute that has not moved in decades. Section 3302 then allows a credit for contributions the employer paid into a certified state unemployment fund, and section 3302(c)(1) caps the total credits at 90 percent of the tax, which is 5.4 percentage points. So the familiar 0.6 percent is the statutory 6 percent net of the maximum credit, and it comes to $42 per employee a year at the wage base.
The credit can be reduced, and it is a real consequence most employers meet only once. Where a state has borrowed from the federal account to pay benefits and has not repaid, section 3302(c)(2) and the provisions following it withdraw part of the credit from employers in that state, so their effective federal rate rises above 0.6 percent until the loan is cleared. It is a state-level condition that lands on individual employers who had no part in creating it.
State financing is not uniform, and the common shorthand is wrong for some workers. The Department of Labor's comparison of state unemployment insurance laws records that all states finance benefits by imposing contributions on employers, and that three states, Alaska, New Jersey and Pennsylvania, also require payment of unemployment taxes by workers, deducted by the employer and remitted with the employer's own taxes. So a flat statement that workers never pay for unemployment insurance is not accurate everywhere. The same document records that in all states an employer's contribution rate is based on its "experience" within the system, which is why a pattern of layoffs raises an employer's cost and why some employers contest claims that they consider disqualifying.
The tax treatment of benefits is where money goes wrong, and it is entirely avoidable. Internal Revenue Code section 85(a) is one sentence: "In the case of an individual, gross income includes unemployment compensation." Benefits are reported to the claimant and to the IRS on Form 1099-G, and nothing is withheld automatically. Section 3402(p)(2) makes withholding voluntary and fixes the rate at a flat 10 percent rather than running it through the graduated system a paycheck uses, and the claimant requests it on Form W-4V. A claimant who does not elect it owes the tax at filing, typically months after the money has been spent on the expenses it was drawn to cover, and often in a year when the household has no reserve left to pay it from. State tax treatment is separate and varies.
A benefits exclusion that a great deal of surviving guidance describes does not exist now. A temporary provision excluded a limited amount of unemployment compensation from income for taxpayers below an income threshold, and its own words confined it to a taxable year beginning in 2020. It has not been renewed. Any explanation suggesting a current-year exclusion is describing a rule that expired, and acting on it produces an understated return.
Coverage gaps follow from who is an employer's employee. The tax and the state programs reach employment, so a worker who is properly classified as an independent contractor generally has neither unemployment insurance nor workers' compensation, which is one of the substantive costs of contracting that a higher rate has to cover. Classification is decided under whichever body of law is asking rather than by what a contract calls the arrangement, so a worker who believes they were misclassified can generally still file a claim and let the state agency decide.