Quick Answer
Step 4 on the W-4 handles complex withholding situations. Use 4(a) to withhold extra tax if you have other income, 4(b) to reduce withholding for large deductions beyond the standard deduction, and 4(c) to specify an exact extra amount per paycheck. Most employees should leave Step 4 blank.
Best Answer
Sarah Chen, Payroll Tax Analyst
Best for employees with complex tax situations like multiple jobs, significant investment income, or large deductions
Understanding Step 4's three sections
Step 4 of the W-4 is the most complex section, designed for employees with tax situations that go beyond a single job and the standard deduction. Most people can leave Step 4 entirely blank, but it's essential for certain situations.
Step 4 has three parts:
Step 4(a): Other Income
Use this section when you have significant income that doesn't have taxes automatically withheld.
Common sources requiring 4(a) entries:
Example: You earn $70,000 from your W-2 job but also receive $8,000 annually in dividend income from investments. Since dividends aren't subject to withholding, you'd enter $8,000 in Step 4(a). Your employer will increase your federal withholding by approximately $308 per biweekly paycheck to cover the additional tax on this income.
Step 4(b): Deductions
This section reduces your withholding when you have deductions significantly larger than the standard deduction ($15,000 single, $30,000 married filing jointly for 2026).
Qualifying deductions for 4(b):
Example calculation: You're single, earn $85,000, and have:
This reduces your federal withholding by approximately $250 per biweekly paycheck.
Step 4(c): Extra Withholding
Use this when you want additional federal tax withheld from each paycheck beyond the calculated amount.
Common reasons for extra withholding:
Example: You're married, both spouses earn $50,000, and you typically owe $1,500 at tax time. To avoid this, enter $58 in Step 4(c) ($1,500 ÷ 26 biweekly pay periods = $57.69). This ensures you break even or get a small refund.
Real-world Step 4 scenarios
When to leave Step 4 blank
Most employees should leave Step 4 completely blank if they:
What you should do
Use the IRS Tax Withholding Estimator before filling out Step 4. This tool considers your complete tax picture and provides specific recommendations for each section. If your situation changes significantly during the year (new rental property, large medical bills, job change), revisit Step 4.
For complex situations involving multiple income sources, consider consulting a tax professional to ensure your withholding strategy aligns with your overall tax planning.
Key takeaway: Step 4 handles complex withholding situations: use 4(a) for other income like investments or rentals, 4(b) for large deductions beyond the standard deduction, and 4(c) for extra withholding per paycheck.
Key Takeaway: Step 4 is for complex tax situations: 4(a) accounts for other income, 4(b) reduces withholding for large deductions, and 4(c) adds extra withholding per paycheck.
Step 4 sections and their common uses
| Step 4 Section | Purpose | Common Examples | Effect on Withholding |
|---|---|---|---|
| 4(a) - Other Income | Income without withholding | Dividends, rental income, side business | Increases withholding |
| 4(b) - Deductions | Large deductions beyond standard | Mortgage interest, charitable giving | Decreases withholding |
| 4(c) - Extra Withholding | Additional tax per paycheck | Avoiding owing taxes, quarterly payments | Increases withholding |
More Perspectives
Sarah Chen, Payroll Tax Analyst
Best for new employees who want to understand Step 4 but likely don't need to use it yet
Why most first-time employees skip Step 4
As someone starting your career, you can almost certainly leave Step 4 blank. This section is designed for complex tax situations that typically develop later in life — multiple income sources, significant investments, or homeownership with large deductions.
When Step 4 might apply to you in the future
Starting a side hustle: If you begin freelancing or selling products online and earn more than $400 annually, you'll need to account for self-employment taxes. You might use Step 4(a) to increase withholding or Step 4(c) to have extra money withheld for quarterly payments.
Getting investment income: Once you start building an investment portfolio generating significant dividends or capital gains, Step 4(a) helps ensure enough tax is withheld throughout the year.
Buying a home: When you become a homeowner with mortgage interest and property taxes exceeding the standard deduction, Step 4(b) can reduce your withholding to account for these larger deductions.
Example of how Step 4 might help later
Suppose in five years you're earning $55,000, bought a condo, and have:
You'd enter $1,000 in Step 4(b), increasing your take-home pay by about $38 per biweekly paycheck.
What you should focus on instead
For now, concentrate on getting Steps 1-3 and Step 5 correct. Make sure you're claiming the right filing status, handling multiple jobs properly (if applicable), and updating your W-4 when you get married or have children.
Key takeaway: New employees should leave Step 4 blank and focus on simpler W-4 sections, but understanding Step 4 prepares you for future complex tax situations involving multiple income sources or large deductions.
Key Takeaway: First-time employees should leave Step 4 blank and focus on basic W-4 sections, but understanding it helps prepare for future complex tax situations.
Sarah Chen, Payroll Tax Analyst
Best for married couples with combined income sources, deductions, or withholding coordination needs
Coordinating Step 4 as a married couple
Married couples filing jointly need to coordinate Step 4 carefully since your combined tax liability depends on total household income and deductions. Generally, it's simpler to handle all Step 4 adjustments on one spouse's W-4 rather than splitting them.
Common married couple Step 4 situations
Investment income: If you have joint investment accounts generating dividends or capital gains, enter the total amount in Step 4(a) on the higher earner's W-4. Don't split it between both forms.
Itemized deductions: Your mortgage interest, property taxes, and charitable contributions benefit your joint return. Calculate your total itemized deductions, subtract the married filing jointly standard deduction ($30,000 for 2026), and enter the excess in Step 4(b) on one W-4.
Example coordination: You and your spouse earn $65,000 and $45,000 respectively, with $5,000 in annual dividend income and $38,000 in itemized deductions.
When both spouses might use Step 4
Vastly different incomes with separate situations: If one spouse has significant self-employment income while the other is a W-2 employee, each might need different Step 4 adjustments.
Extra withholding for peace of mind: If you consistently owe taxes, both spouses might add small amounts to Step 4(c). For example, if you want $2,000 extra withheld annually, one spouse could enter $77 in Step 4(c).
What you should do
Use the IRS Tax Withholding Estimator with both spouses' information to get personalized Step 4 recommendations. This tool considers your combined tax picture and suggests which spouse should make adjustments and in what amounts.
Key takeaway: Married couples should coordinate Step 4 adjustments on one spouse's W-4 (usually the higher earner) to account for combined other income, joint deductions, or extra withholding needs.
Key Takeaway: Married couples should typically handle all Step 4 adjustments on one spouse's W-4 to properly coordinate their combined income, deductions, and withholding needs.
Sources
- IRS Publication 15-T — Federal Income Tax Withholding Methods
- IRS Tax Withholding Estimator — Tool for calculating optimal withholding amounts
Related Questions
Reviewed by Sarah Chen, Payroll Tax Analyst on February 28, 2026
This content is for educational purposes only and is not a substitute for professional tax advice. Consult a qualified tax professional for advice specific to your situation.