The basic formula: gross pay minus withholdings

Payroll tax calculation starts with gross pay — the total amount an employee earns before any deductions. From that, you subtract federal income tax withholding, Social Security tax, Medicare tax, and any state or local income taxes that explore. The result is net pay, what the employee actually receives.

The withholding amounts depend on three things: the employee's W-4 form (which tells you how many allowances they claim), their pay frequency, and tax tables published by the IRS each year. You are not calculating the employee's final tax bill — you are calculating what to hold back from each paycheck and send to the government.

As the employer, you also owe a matching portion of Social Security and Medicare tax, plus federal and state unemployment insurance. These are separate from what you withhold from the employee's pay.

Key Takeaways

  • Federal income tax withholding depends on the W-4 form the employee completed, their pay frequency, and IRS tax tables that change each year.
  • Social Security tax is 6.2% of gross pay (up to an annual wage cap that changes yearly), and Medicare tax is 1.45% with no cap.
  • You must match the employee's Social Security and Medicare contributions, and you owe separate employer taxes for federal and state unemployment insurance.
  • The IRS provides free tax tables and a withholding calculator; many payroll software packages handle the math automatically.
  • State and local income tax withholding varies by location and must be calculated separately using your state's tax tables.

Federal income tax withholding using the W-4

When an employee starts, they complete Form W-4 (Employee's Withholding Certificate). This form tells you how much federal income tax to withhold from each paycheck. The employee claims a number of allowances based on their personal situation — dependents, second jobs, spouse's income, and other factors.

The IRS publishes tax withholding tables each year in Publication 15-T. These tables cross-reference the employee's pay frequency (weekly, biweekly, monthly, etc.), their gross pay, and their W-4 allowances to give you the exact withholding amount. You can also use the IRS tax withholding calculator on irs.gov, which walks through the employee's situation and produces a recommended W-4.

If an employee's circumstances change — they marry, have a child, take a second job, or their spouse starts working — they should file a new W-4. You are not required to ask them to update it, but if they do, the new withholding takes effect on the next paycheck.

Social Security and Medicare taxes (FICA)

FICA taxes (Federal Insurance Contributions Act) consist of two parts: Social Security and Medicare. These are calculated as a percentage of gross pay, and you withhold them from the employee's paycheck and match them from your own funds.

Social Security tax is 6.2% of gross pay, but only on earnings up to an annual wage cap. That cap changes each year — for 2024 it is $168,600, but confirm the current year's figure on ssa.gov. Once an employee's year-to-date earnings hit that cap, you stop withholding Social Security tax for the rest of the year (though you continue Medicare). Medicare tax is 1.45% of all gross pay with no cap. Employees earning over $200,000 (or $250,000 if married filing jointly) owe an additional 0.9% Medicare tax on the excess, which you must withhold.

You match both percentages from your own funds. So if an employee pays 6.2% Social Security, you also pay 6.2% as the employer. This matching obligation exists whether or not the employee's withholding is correct — it is a separate employer tax.

State and local income tax withholding

Most states impose income tax, and some cities do as well. Each state publishes its own tax tables and withholding rules, similar to the federal system. You must obtain your state's tax tables and follow their instructions for calculating withholding.

Some states use a percentage-based system; others use tables like the federal IRS. A few states have no income tax at all (Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington, Wyoming). If you have employees in multiple states, you must withhold according to each state's rules — the state where the employee works, not where your business is located.

Local income taxes vary widely. Some cities tax all residents and workers; others tax only residents. Check with your city or county tax authority to learn the rate and whether you must withhold it.

Employer taxes: unemployment insurance and payroll tax matching

Beyond withholding from employee paychecks, you owe employer taxes. Federal Unemployment Tax Act (FUTA) tax is 6% of the first $7,000 of each employee's annual wages (the rate and wage base can vary). Most employers receive a credit of up to 5.4% if they pay state unemployment tax on time, bringing the effective federal rate to 0.6%.

State Unemployment Insurance (SUI) tax rates vary by state and by industry. New employers often pay a standard rate; established employers pay a rate based on their history of claims. You pay SUI on a portion of each employee's wages — the wage base varies by state but is often $7,000 to $10,000 per employee per year.

You also owe the employer match for Social Security (6.2%) and Medicare (1.45%), calculated the same way as the employee withholding. These are not withheld from the employee — they come from your business funds.

Using payroll software or a payroll service

Most small businesses use payroll software (QuickBooks Payroll, Gusto, ADP, Paychex) or hire a payroll service provider to handle these calculations. The software stores each employee's W-4, gross pay, and state/local information, then applies the current tax tables automatically. This reduces errors and keeps you compliant as tax rates and wage caps change each year.

If you calculate payroll manually, you must update your tax tables every January and whenever the IRS or your state publishes changes. The IRS publishes updated Publication 15-T and tax tables on irs.gov; your state tax authority publishes state tables on its website. Manual calculation is error-prone and time-consuming for more than a handful of employees.

Whether you use software or a service, you remain responsible for accuracy. The IRS and your state can assess penalties and interest if withholding is incorrect, even if a vendor made the error.

Reconciling and depositing taxes throughout the year

You do not send taxes to the government with each paycheck. Instead, you deposit withheld taxes on a schedule set by the IRS based on your total tax liability. Most employers deposit federal taxes semi-weekly or monthly using the Electronic Federal Tax Payment System (EFTPS) or through their bank's bill-pay system.

At the end of the year, you file Form 941 (Employer's Quarterly Federal Tax Return) each quarter to reconcile what you withheld and paid against what you owed. You also file Form 940 (Employer's Annual Federal Unemployment Tax Return) to report FUTA tax. State and local taxes have their own filing schedules and forms.

If you withheld too much, you receive a refund or credit. If you withheld too little, you owe the difference plus potential penalties. Accuracy in each paycheck prevents large surprises at year-end.

Common mistakes and how to avoid them

The most common error is using outdated tax tables. Tax tables change every January and sometimes mid-year. If you use last year's tables, your withholding will be wrong. Set a calendar reminder to read the new tables on January 1 and check the IRS website monthly for updates.

Another frequent mistake is confusing employee withholding with employer taxes. You withhold federal income tax, Social Security, and Medicare from the employee's pay. You separately owe employer Social Security, Medicare, FUTA, and SUI from your own funds. Both must be calculated and deposited on time.

Failing to update a W-4 when an employee's situation changes can lead to under-withholding and a tax bill for the employee at year-end. Encourage employees to update their W-4 whenever their circumstances shift, and keep copies on file.

Frequently Asked Questions

What if an employee claims too many allowances on their W-4?

The IRS does not limit the number of allowances an employee can claim. If they claim too many, federal income tax withholding will be too low, and they will owe money at tax time. You are not responsible for the employee's final tax bill — only for withholding according to their W-4. If you suspect fraud, you can report it to the IRS, but this is rare.

Do I have to withhold taxes for an independent contractor?

No. Independent contractors are responsible for their own taxes. You do not withhold federal income tax, Social Security, or Medicare. You do report payments over $600 to a contractor on Form 1099-NEC. Misclassifying an employee as a contractor can result in back taxes and penalties, so confirm the worker's status carefully.

What happens if I deposit taxes late?

The IRS charges a penalty based on how late the deposit is — 2% if one to five days late, 5% if six to fifteen days late, and 10% if more than fifteen days late. Interest also accrues on the unpaid amount. Set up automatic deposits or calendar reminders to avoid this.

Do I need to withhold taxes for employees who work part-time or seasonally?

Yes. Withholding rules explore to all employees regardless of hours or tenure. Part-time and seasonal workers complete a W-4 and receive the same withholding treatment as full-time staff. You still owe employer taxes (FUTA, SUI, and matching FICA) for them as well.

Where do I find my state's tax withholding tables?

Each state tax authority publishes withholding tables and instructions on its website. Search "[your state] income tax withholding" or visit your state's department of revenue website. If your state has no income tax, you withhold only federal and local taxes (if applicable).