What payroll taxes are and why you calculate them

Payroll taxes are the federal, state, and sometimes local taxes withheld from an employee's paycheck and paid to the government. As an employer or payroll administrator, you calculate these taxes based on the employee's gross pay, their filing status, and the number of dependents they claim. The calculation determines how much money leaves the paycheck and goes to the IRS, your state revenue department, and possibly your city.

You perform this calculation for every pay period — weekly, biweekly, semimonthly, or monthly, depending on your payroll schedule. The amount withheld is not a flat percentage; it changes based on the employee's W-4 form, which they fill out when hired and can update at any time.

Payroll taxes are separate from income tax withholding. They include Social Security tax (6.2% of gross pay up to an annual wage cap), Medicare tax (1.45% of all gross pay), and federal income tax withholding (which varies by person). Some states and cities add their own income taxes on top.

Key Takeaways

  • Payroll tax calculation starts with gross pay and uses the employee's W-4 form, current tax tables, and their filing status to determine federal income tax withholding.
  • Social Security tax is 6.2% of gross pay up to the annual wage base (which changes yearly), and Medicare tax is 1.45% of all gross pay with no cap.
  • The IRS publishes updated tax withholding tables and a calculator tool each year; using outdated tables will produce incorrect withholding amounts.
  • State and local income taxes are calculated separately using each jurisdiction's own tax tables and rates, which vary widely by location.
  • Most payroll software automates these calculations, but understanding the steps helps you catch errors and know what employees are seeing on their pay stubs.

Step 1: Gather the employee's W-4 form and current tax tables

Before you calculate anything, you need two pieces of information: the employee's Form W-4 (Employee's Withholding Certificate) and the current year's IRS tax withholding tables. The W-4 tells you the employee's filing status (single, married, head of household), the number of dependents or other adjustments they claim, and whether they want extra withholding.

The IRS publishes new tax tables every year, usually in late December for the following year. These tables are organized by pay frequency (weekly, biweekly, semimonthly, monthly) and filing status. You can find them on the IRS website under "Publication 15-T" or use the IRS withholding calculator at irs.gov. Do not use last year's tables — tax brackets and standard deductions change annually, and using old tables will produce incorrect withholding.

If an employee has not filled out a W-4, they are treated as single with no dependents claimed, which usually results in higher withholding. Ask them to complete one as soon as possible.

Step 2: Calculate gross pay for the pay period

Gross pay is the total amount owed before any deductions. For hourly employees, multiply the hourly rate by the hours worked in the pay period. For salaried employees, divide the annual salary by the number of pay periods in a year. Include any bonuses, overtime, or commissions earned during that pay period.

Example: An employee paid biweekly at $20 per hour who worked 80 hours earns $1,600 gross. A salaried employee earning $52,000 per year paid biweekly earns $2,000 per pay period ($52,000 ÷ 26 pay periods).

Gross pay is the starting point for all tax calculations. Deductions like health insurance premiums or 401(k) contributions may reduce the amount subject to federal income tax withholding (called "taxable wages"), but they do not reduce the amount subject to Social Security and Medicare taxes.

Step 3: Calculate federal income tax withholding using the W-4 and tax tables

Federal income tax withholding is the most complex calculation because it depends on the employee's W-4 entries and the IRS tax tables for their pay frequency and filing status. The process has two parts: calculate the tentative withholding using the tax tables, then apply any adjustments from the W-4.

Using the IRS tax tables: Find the table for your pay frequency and the employee's filing status. Locate the row that matches the employee's taxable wages (usually the same as gross pay unless pre-tax deductions apply). The table shows the withholding amount. For example, if an employee is single, paid biweekly, and has $1,600 in taxable wages, the 2024 table might show $145 in federal withholding (this is an example; actual amounts vary by year).

Apply W-4 adjustments: If the employee claimed dependents or other adjustments on their W-4, subtract those amounts from the tentative withholding. If they requested extra withholding, add that amount. The result is the federal income tax withheld from that paycheck.

Alternatively, use the IRS withholding calculator at irs.gov/taxes/individuals/tax-withholding-estimator. You enter the employee's information once, and it produces a recommended W-4 entry. Some employers use this to help employees adjust their withholding if they are getting large refunds or owing money at tax time.

Step 4: Calculate Social Security and Medicare taxes

Social Security tax is 6.2% of gross pay, but only up to the annual wage base. The wage base changes every year (in 2024 it was $168,600; check the IRS website for the current year). Once an employee's cumulative gross pay reaches that cap in a calendar year, you stop withholding Social Security tax for the rest of that year.

Example: An employee earning $3,500 biweekly has $3,500 × 0.062 = $217 in Social Security tax withheld. If by November they have already earned $168,600 for the year, their final paychecks that year will have $0 Social Security tax because they have hit the cap.

Medicare tax is 1.45% of all gross pay with no annual cap. It is withheld every pay period for the entire year. Additionally, employees earning over $200,000 (single) or $250,000 (married filing jointly) in a calendar year owe an extra 0.9% Medicare tax on wages above those thresholds. This is called the Additional Medicare Tax and is withheld by the employer.

Example: An employee with $1,600 gross pay has $1,600 × 0.015 = $24 in Medicare tax withheld (1.45% + the 0.9% additional tax if they exceed the income threshold).

Step 5: Calculate state and local income taxes

State income tax withholding varies dramatically by location. Some states have no income tax at all (Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington, Wyoming). Others have flat tax rates (Colorado, Illinois, Indiana, Kentucky, Massachusetts, Michigan, North Carolina, Pennsylvania). Still others use progressive tax brackets similar to federal taxes.

Each state publishes its own tax tables and withholding forms. Some states use a W-4 equivalent; others use a different form or allow employees to claim exemptions differently. You must obtain the correct form and tables for each state where you have employees.

Local income taxes (city or county) exist in some jurisdictions and are calculated separately using local tax tables. For example, New York City, Philadelphia, and Columbus, Ohio all have local income taxes. If you have employees in these areas, you must withhold and remit local tax in addition to state tax.

The safest approach is to check your state's department of revenue website for the current withholding tables and instructions. Many payroll software providers include state and local tax tables and update them automatically each year.

Step 6: Deduct pre-tax contributions and other withholdings

After calculating income and payroll taxes, deduct any pre-tax contributions the employee has authorized. These reduce the employee's take-home pay but do not reduce the amount subject to Social Security and Medicare taxes. Common pre-tax deductions include health insurance premiums, 401(k) contributions, and dependent care account contributions.

Post-tax deductions (like Roth 401(k) contributions, garnishments, or union dues) are withheld after taxes are calculated and do not reduce taxable income. The order matters: calculate all taxes first, then deduct pre-tax items, then deduct post-tax items.

Example: An employee with $1,600 gross, $145 federal withholding, $217 Social Security, $24 Medicare, $80 state tax, and $100 in 401(k) contributions receives $1,600 − $145 − $217 − $24 − $80 − $100 = $1,034 net pay.

Using payroll software versus manual calculation

Most employers use payroll software (ADP, Gusto, Paychex, QuickBooks Payroll) or hire a payroll service to perform these calculations automatically. The software stores each employee's W-4 and tax information, updates tax tables annually, and calculates withholding for every pay period. This reduces errors and saves time, especially for businesses with many employees or employees in multiple states.

If you calculate payroll manually, you must update your tax tables every January and track each employee's year-to-date earnings to know when they hit the Social Security wage base cap. Manual calculation is error-prone and time-consuming, but understanding the steps helps you verify that your software or payroll service is producing correct results.

Regardless of the method, you are responsible for remitting withheld taxes to the IRS and your state on time. The IRS publishes a deposit schedule (monthly or semiweekly, depending on your payroll size) that tells you when payments are due. Missing a deposit deadline results in penalties and interest.

Frequently Asked Questions

What is the difference between gross pay and taxable wages?

Gross pay is the total amount owed before any deductions. Taxable wages are the amount subject to federal income tax withholding after certain pre-tax deductions (like 401(k) contributions or health insurance premiums) are removed. Social Security and Medicare taxes are always calculated on gross pay, not taxable wages.

Do I have to recalculate withholding if an employee updates their W-4?

Yes. When an employee submits a new W-4, you must begin using the new information on the next pay period. Do not recalculate past paychecks unless there was an error. If an employee claims more dependents, their withholding will decrease; if they claim fewer, it will increase.

What happens if I withhold the wrong amount?

If you withhold too little, the employee may owe money when they file their tax return. If you withhold too much, they receive a refund. Either way, the employee can adjust their W-4 to change their withholding for future pay periods. The IRS also allows employers to correct significant withholding errors by adjusting future paychecks.

Do I withhold payroll taxes for independent contractors?

No. Independent contractors are responsible for paying their own income and self-employment taxes. You issue them a Form 1099-NEC instead of a W-2 and do not withhold anything from their payments. However, if a contractor earns over $600 in a calendar year, you must report it to the IRS.

Where do I find the current year's tax tables and wage base limits?

The IRS publishes tax tables and withholding guidance on irs.gov. Look for Publication 15-T (Federal Income Tax Withholding Methods) and Publication 15 (Circular E, Employer's Tax Guide). Your state's department of revenue website has state tax tables. The Social Security Administration publishes the annual wage base limit on ssa.gov.