What Payroll Taxes Employers Calculate

Employers calculate and withhold four separate payroll taxes from each employee's paycheck: federal income tax, Social Security tax, Medicare tax, and state income tax (in most states). The employer also pays a matching amount for Social Security and Medicare on top of what comes out of the employee's check. These are not optional — federal law requires employers to withhold and remit them on a set schedule, usually monthly or semi-weekly depending on the size of the payroll.

The calculation starts with gross pay — the total amount an employee earned before any deductions. From there, the employer subtracts pre-tax deductions (like health insurance premiums or 401(k) contributions), then applies tax rates to what remains. The result is the net pay the employee actually receives, plus a separate bill the employer owes to the IRS and state tax authorities.

Key Takeaways

  • Federal income tax withholding is calculated using the employee's W-4 form, their pay frequency, and IRS withholding tables or the IRS tax calculator.
  • Social Security tax is 6.2% of gross pay up to an annual wage cap (which changes yearly), and Medicare tax is 1.45% of all gross pay with no cap.
  • Employers pay an equal matching amount for Social Security and Medicare on top of employee withholding, doubling the total tax burden on payroll.
  • State income tax rates and rules vary widely by state; some states have no income tax, while others use different calculation methods than the federal system.
  • Payroll tax deposits are due on a schedule set by the IRS based on how much tax the employer owes, typically monthly or semi-weekly.

Federal Income Tax Withholding

Federal income tax withholding begins with the W-4 form, which the employee fills out when hired. The W-4 tells the employer how many withholding allowances the employee claims — this number directly affects how much tax is withheld from each paycheck. An employee who claims zero allowances will have more withheld; an employee who claims many allowances will have less.

The employer then uses the employee's gross pay, the number of allowances claimed, and the IRS withholding tables (or the IRS tax calculator) to determine the exact dollar amount to withhold. The calculation depends on pay frequency: an employee paid weekly will have a different withholding amount than one paid monthly, even if their annual salary is the same. The IRS updates these tables and calculators yearly, so the withholding amount can change even if the employee's W-4 does not.

If an employee's life changes — they get married, have a child, take a second job, or their spouse starts working — they can file a new W-4 to adjust their withholding. This is voluntary; the employee initiates it, not the employer.

Social Security and Medicare Tax

Social Security tax is 6.2% of the employee's gross pay, but only up to a wage cap that the IRS sets each year. Once an employee's pay reaches that cap in a calendar year, no more Social Security tax is withheld for the rest of that year. The employer also pays 6.2% as a matching contribution. Medicare tax is 1.45% of all gross pay with no wage cap — it applies to every dollar earned, all year long. The employer matches this 1.45% as well.

Employees earning over $200,000 per year (or $250,000 for married couples filing jointly) pay an additional 0.9% Medicare tax on income above that threshold. This is called the Additional Medicare Tax, and the employer withholds it but does not match it — only the employee pays this portion.

The employer's matching contributions are a separate cost to the business. If an employee's gross pay is $1,000, the employer withholds $62 for Social Security and $14.50 for Medicare from the employee's check, but the employer also owes $62 and $14.50 to the IRS as its own contribution. This is why payroll is expensive for employers even before salaries themselves.

State Income Tax Withholding

State income tax rules vary significantly by location. Some states have no income tax at all (including Florida, Texas, and Wyoming), so employers in those states do not withhold state income tax. Other states use a flat tax rate — a single percentage applied to all income. Still others use a progressive system with multiple tax brackets, similar to the federal system.

Employees typically fill out a state W-4 or equivalent form when hired, which tells the employer how much state tax to withhold. Some states use the federal W-4 information; others require a separate state form. The employer then applies the state's tax rate or tables to the employee's pay, just as they do for federal tax.

If an employee works in one state but lives in another, the rules become more complex. Generally, the employee pays income tax to the state where they work, though some states have reciprocal agreements that change this. Employers need to know the employee's work location to withhold the correct state tax.

The Order of Deductions

Payroll taxes are not all withheld from the same amount. The calculation follows a specific order: gross pay, then pre-tax deductions (like health insurance or 401(k) contributions), then federal income tax, then Social Security and Medicare taxes, then state income tax, then any post-tax deductions (like garnishments or union dues).

This matters because pre-tax deductions reduce the amount subject to federal income tax and state income tax, but Social Security and Medicare taxes are calculated on the full gross pay before pre-tax deductions are subtracted. For example, if an employee earns $2,000 and contributes $200 to a 401(k), federal income tax is calculated on $1,800, but Social Security and Medicare are calculated on $2,000.

Payroll Tax Deposits and important date

Once an employer calculates and withholds payroll taxes, those taxes must be deposited with the IRS and the state on a schedule. The IRS sets deposit important date based on how much tax the employer owes. Most employers deposit monthly — taxes withheld during a month are due by the 15th of the following month. Larger employers may be required to deposit semi-weekly or even more frequently.

Employers use the Electronic Federal Tax Payment System (EFTPS) or an authorized payment processor to deposit federal taxes. State taxes are deposited through each state's tax authority, using methods that vary by state. Missing a deposit important date results in penalties and interest, so employers track these dates carefully.

At the end of the year, employers file Form 941 (quarterly) or Form 944 (annually, for small employers) to reconcile the taxes they withheld and deposited with what they actually owed. If they over-withheld, they get a credit; if they under-withheld, they owe the difference.

Common Payroll Tax Mistakes

One frequent error is misclassifying workers as independent contractors when they should be employees. Contractors do not have payroll taxes withheld; the business pays them a 1099 and the contractor handles their own taxes. Misclassifying an employee as a contractor means the employer fails to withhold required taxes, which creates a liability when the IRS audits.

Another mistake is failing to update W-4 forms when employees' circumstances change. If an employee claims too many allowances and under-withholds, they may owe taxes at the end of the year. If they claim too few and over-withhold, they get a refund — but the employer has used their money interest-free all year.

Employers also sometimes forget that the wage cap for Social Security tax changes yearly. If they do not update their payroll system, they may continue withholding Social Security tax after an employee has reached the cap, which requires a correction and refund later.

Frequently Asked Questions

What is the difference between what the employer withholds and what the employer pays?

The employer withholds federal income tax, Social Security, and Medicare from the employee's paycheck — this money comes out of the employee's pay. The employer also pays a matching amount for Social Security and Medicare from its own funds. These are two separate costs. The employee sees the withholding on their stub; the employer's matching contribution is a business expense the employee does not see.

Do employers have to use the IRS withholding tables, or can they calculate it differently?

Employers must use the IRS withholding tables or the IRS tax calculator to determine federal income tax withholding. The IRS publishes these tables and updates them yearly. Using a different method is not permitted and can result in penalties if the withholding is incorrect.

What happens if an employer withholds the wrong amount of tax?

If the employer withholds too much, the employee gets a refund when they file their tax return. If the employer withholds too little, the employee owes taxes at filing time. The employer is responsible for using the correct W-4 information and current IRS tables; if they make a mistake, they may owe penalties to the IRS.

Are payroll taxes the same for all employees, or do they vary by job title?

Payroll taxes are the same regardless of job title — they depend on gross pay, filing status (from the W-4), and location. A manager and an entry-level employee earning the same salary pay the same payroll taxes. The only variation is in federal income tax withholding, which depends on the W-4 the employee files.

Can an employer choose not to withhold payroll taxes to save money?

No. Payroll tax withholding is required by federal law. An employer that does not withhold and deposit these taxes faces serious penalties, interest, and potential criminal charges. The IRS treats unpaid payroll taxes as a high-priority collection matter.