Form W-4: What Employers Need to Know

By Nicole Hullihen, former SaaS Chief Operating Officer and Microsoft MVP · Updated October 18, 2026

Every new hire fills out a Form W-4, and most small business owners hand it over without a second thought. But the W-4 controls how much federal income tax comes out of each paycheck, and the IRS has specific rules for employers: when to collect it, what to do when it's missing or filled out wrong, how quickly to apply changes and how long to keep it.

This guide walks through those rules in plain language, with examples, a step-by-step process and a checklist. It's written for owners and managers who work with a payroll provider or accountant and want to understand what's happening and what they're responsible for.

Note: This is general information, not tax advice. Tax rules change, and the IRS updates the W-4 and its instructions regularly. Use the current form and IRS guidance, and check with your payroll provider or tax professional about your situation. Many states have their own withholding forms as well.

What Form W-4 Does

The IRS explains that Form W-4 is completed by employees and given to their employer so the employer can withhold the correct federal income tax from the employee's pay. The employer uses the employee's Form W-4 and the appropriate withholding table in IRS Publication 15-T to figure the amount.

A few things the W-4 does not control:

• Social Security and Medicare taxes. The IRS says employers generally must withhold these from employees' wages, and employers also pay their own share. The W-4 doesn't change them.
• State income tax. Many states have their own withholding certificate. Check your state's rules.
• Other deductions such as benefits or garnishments. See wage garnishment: what employers need to know.

The Five Steps on the Current W-4

According to the IRS, the only steps required for all employees are Step 1 and Step 5. Steps 2 through 4 apply only if they're relevant to the employee.

Employees decide what to enter. The IRS notes that employees can account for other income in Step 4(c) as extra withholding without reporting that income to their employer, or pay estimated tax directly instead. Employers generally shouldn't try to tell employees what to put on the form. If an employee asks for help, point them to the form instructions or the IRS Tax Withholding Estimator.

When to Collect a W-4

The IRS says that when you hire an employee, you must have the employee complete a Form W-4. Build it into your onboarding so it's collected on or before the first day of work, along with Form I-9. See Form I-9: how to complete it correctly and the new hire orientation checklist.

If an Employee Doesn't Turn In a W-4

The IRS says that if an employee doesn't give you a properly completed Form W-4, you should withhold as if the employee is single or married filing separately, with no entries in Steps 2, 3 or 4. In practice, that often means more tax is withheld than the employee might want, which gives them a reason to turn the form in.

When a New W-4 Takes Effect

Employees can submit a new W-4 when their situation changes, such as marriage, a new baby or a second job. According to the IRS, you must put a new W-4 into effect no later than the start of the first payroll period ending on or after the 30th day from the date you receive it, unless the invalid form or lock-in letter rules apply.

Employees Who Claim Exempt

Some employees claim exemption from federal income tax withholding. The IRS says an exempt W-4 is valid only for the calendar year in which it's furnished. To keep exempt status, the employee must give you a new W-4 by February 15 of the next year.

• If the employee doesn't renew: the IRS says to withhold as if the employee is single, with no other entries in Steps 2 through 4. Remind employees before the deadline so this doesn't come as a surprise.
• If a new exempt form arrives on or after February 16: apply it to future wages only. The IRS says not to refund taxes withheld while the exempt status wasn't in place.
• Remind exempt employees each January so they aren't surprised by a change in their paycheck.

Invalid W-4s

The IRS says any unauthorized change or addition to Form W-4 makes it invalid. If you receive an invalid form:

1. Don't use it.
2. Tell the employee it's invalid and ask for a new one.
3. If the employee doesn't provide a valid form, keep withholding based on their last valid W-4. If there isn't one, withhold at the default rate (single or married filing separately with no other entries).

Lock-In Letters

Sometimes the IRS determines that an employee doesn't have enough tax withheld and sends the employer a lock-in letter that sets a specific withholding level. According to the IRS:

• You must disregard any W-4 that would decrease withholding below the lock-in letter amount.
• You must honor any W-4 that results in more income tax withheld.
• Lock-in rules can apply to employees you rehire within 12 months.
• Electronic W-4 systems must not let employees reduce withholding below the lock-in amount.

Follow the instructions in the letter, and work with your payroll provider to apply it.

Employees Hired Before 2020

The W-4 was redesigned in 2020. The IRS says employees who had a W-4 on file before then aren't required to furnish a new form just because of the redesign, and employers must continue to withhold based on the forms previously furnished. You can ask these employees to submit a new form, but the IRS says the request should explain that they aren't required to, and that withholding will continue based on their prior form if they don't.

Recordkeeping

The IRS says to keep the signed W-4 for at least 4 years, have it available for IRS inspection and be able to provide a hardcopy of any form received electronically. More broadly, the IRS says to keep all records of employment taxes for at least 4 years. See payroll report requirements for small business.

The IRS also says employers may be directed to send certain W-4s to the IRS by written notice or future guidance. Otherwise, the W-4 stays in your files.

Storage Tips

• Store W-4s securely, since they include Social Security numbers.
• Keep current and prior versions for each employee.
• Note the date each form was received, which matters for the effective date rule.
• Limit access to people who handle payroll.

Step-by-Step W-4 Process for Small Businesses

1. Give new hires the current Form W-4 with onboarding paperwork.
2. Collect the signed form on or before the first day.
3. Check that Step 1 and Step 5 are complete and the form hasn't been altered.
4. Send the information to your payroll provider or enter it in your payroll system.
5. Date-stamp and file the form securely.
6. Apply changes from new W-4s within the IRS timing rule.
7. Remind exempt employees each January about the February 15 deadline.
8. Follow any lock-in letters you receive.
9. Keep forms for at least 4 years.

Common W-4 Mistakes

• Not collecting a W-4 at hire.
• Guessing withholding when the form is missing instead of using the default.
• Telling employees what to enter on the form.
• Accepting altered forms.
• Letting exempt status roll over past February 15 without a new form.
• Requiring pre-2020 employees to fill out a new form.
• Ignoring lock-in letters.
• Losing forms or not keeping them for 4 years.
• Forgetting state withholding forms.

Form W-4 Checklist

Answering Common Employee Questions

Employees often ask managers for help with the W-4. It's fine to explain the process, but avoid giving tax advice. Helpful responses:

Paper vs. Electronic W-4s

Many payroll systems let employees complete the W-4 electronically. If you use an electronic system, the IRS says you must be able to provide a hardcopy of any electronic W-4, and the system must follow IRS rules, including not allowing employees to reduce withholding below a lock-in letter amount. Ask your payroll provider whether its system meets these requirements.

Year-End Reminders

January is a good time to send every employee a short note: if their situation changed during the year, they can submit a new W-4, and anyone who claimed exempt needs a new form by February 15. A simple reminder prevents surprises in February paychecks.

Example: A Mid-Year Change

A server at a small restaurant gets married in May and hands the owner a new W-4 claiming married filing jointly. The owner date-stamps the form, sends it to the payroll provider the same day and files the signed copy. The provider applies it on the next payroll, which is well within the IRS 30-day timing rule. The old form stays in the file too, since the owner keeps W-4 records for at least 4 years.

Quick Reference

Give Your Payroll Provider Clean Data With Updoot

Withholding is only as accurate as the hours and pay it's based on. Updoot's employee time clock records every hour, and the payroll report gives your payroll provider or accountant clean totals for regular time, overtime and PTO each pay period. Updoot creates the payroll report; your payroll provider handles the withholding. SOP management keeps your onboarding steps, including the W-4, in one checklist.

Sources

• IRS: About Form W-4, Employee's Withholding Certificate
• IRS: Topic No. 753, Form W-4, Employee's Withholding Certificate
• IRS: FAQs on the 2020 Form W-4
• IRS: Publication 15, Employer's Tax Guide
• IRS: Understanding Employment Taxes

Frequently Asked Questions