How to Fill Out W-4 Line 4b: 2026 Deductions Worksheet

To fill out Line 4b on your W-4, enter the amount by which your expected deductions for the year exceed your standard deduction, using the Deductions Worksheet on page 4 of the form to arrive at the figure. For 2026, the standard deduction is $16,100 for single filers, $32,200 for married filing jointly, and $24,150 for head of household, so your itemized and above-the-line deductions have to clear those thresholds before Line 4b produces a number worth entering.¹

What Line 4b Is Actually Telling Payroll

Leave Line 4b blank and your employer’s payroll system withholds tax as if you will claim the standard deduction and nothing more. Enter a dollar amount and payroll treats that much additional income as sheltered from tax, which lowers the withholding on every check. The figure is not your total deductions. It is only the excess over your standard deduction, and it has to come from the worksheet rather than a rough guess.²

Line 4b is worth filling out if you carry a mortgage, pay significant state and local taxes, make large charitable gifts, or have substantial above-the-line deductions like HSA or traditional IRA contributions. If none of that describes you, skip it. Overstating the number is the main risk, because too little withholding can leave you owing tax and a penalty when you file.

Working Through the 2026 Deductions Worksheet

The worksheet on page 4 of the W-4 walks you through each category of deduction, adds them up, and subtracts your standard deduction at the end. The remainder — if there is one — goes on Line 4b. The 2026 version looks different from prior years because the One, Big, Beautiful Bill Act added several new deductions at the top.²

Tips, Overtime, and Vehicle Loan Interest

The first three lines cover deductions that did not exist before 2025. Each has a hard income cutoff, and exceeding the threshold means you get nothing for that line.

Line 1a, qualified tips: up to $25,000 if total income is under $150,000 ($300,000 married filing jointly).
Line 1b, qualified overtime: the “half” portion of your time-and-a-half pay, up to $12,500 ($25,000 married filing jointly), under the same income limits.
Line 1c, vehicle loan interest: up to $10,000 in interest on a passenger vehicle loan if total income is under $100,000 ($200,000 married filing jointly).

Add the three together on Line 2. If none apply, enter zero and keep going.

Senior Add-On

Line 3a lets a taxpayer age 65 or older with total income below $75,000 ($150,000 married filing jointly) enter an additional $6,000. This sits on top of the regular standard deduction bump seniors already receive.²

Itemized and Above-the-Line Amounts

The worksheet then asks for your estimated itemized deductions (the Schedule A total) plus any above-the-line deductions and the qualified business income deduction. These are the traditional entries most people think of first, and the section below covers what to include.

Subtracting the Standard Deduction

After totaling everything, subtract your applicable standard deduction:¹

Single or married filing separately: $16,100
Married filing jointly: $32,200
Head of household: $24,150

If the result is zero or negative, leave Line 4b blank. If it is positive, that number goes on Line 4b. A single filer expecting $24,100 in total deductions would enter $8,000 ($24,100 minus $16,100).

Which Deductions Feed the Worksheet

Not every deduction moves the needle the same amount. Some carry caps, others have income phaseouts, and a few have floors that eat the first several thousand dollars before anything counts.

State and Local Taxes

The SALT deduction covers state or local income taxes (or sales taxes — you pick one), plus property taxes. Starting in 2025, the cap rose from $10,000 to $40,000 ($20,000 if married filing separately), with small annual bumps through 2029. It phases out for modified adjusted gross income above $500,000 ($250,000 married filing separately).³ This change alone is why many taxpayers who took the standard deduction from 2018 through 2024 now benefit from itemizing again.

Home Mortgage Interest

Interest is deductible on up to $750,000 of mortgage debt used to buy, build, or substantially improve your home ($375,000 if married filing separately). Mortgages taken out before December 16, 2017, keep the older $1 million limit, and a refinance of a pre-2017 loan generally carries the higher limit forward as long as the new balance does not exceed the old one.⁴

Charitable Contributions

Cash gifts to qualifying charities are deductible up to 60% of adjusted gross income. Donations of appreciated property like stock or real estate are typically limited to 30% of AGI. Estimate what you realistically expect to give, not what you hope to give. Overstating charitable gifts is one of the quickest ways to end up under-withheld.⁵

Medical and Dental Expenses

Only the portion of unreimbursed medical and dental expenses that exceeds 7.5% of your AGI is deductible. On an $80,000 AGI, the first $6,000 does nothing. This line matters mainly in a year with a major surgery, ongoing treatment, or expensive prescriptions.⁶

Above-the-Line Deductions

These reduce AGI directly and do not require itemizing, but they still belong on the worksheet because they shelter income the payroll system would otherwise tax. The common ones for 2026:

HSA contributions: up to $4,400 for self-only coverage or $8,750 for family coverage.⁷
Traditional IRA contributions: up to $7,500, or $8,600 if you are 50 or older, subject to workplace plan and income rules.⁸
Student loan interest: up to $2,500 per year, phased out at higher incomes.⁹
Educator expenses: up to $300 per qualifying teacher, or $600 if both spouses are eligible educators filing jointly.¹⁰

Do not include alimony if the divorce or separation agreement was finalized after 2018. It is no longer deductible.¹¹

Qualified Business Income Deduction

Income from a sole proprietorship, S corporation, or partnership may qualify for a deduction of up to 20% of that business income. It is taken in addition to either the standard or itemized deduction, and it belongs on the worksheet because it shelters income beyond what payroll already assumes.

If You or Your Spouse Have More Than One Job

Fill in Steps 3 through 4(b) on the W-4 for the highest-paying job only. Leave those steps blank on every other W-4. Splitting the deduction amount across multiple forms produces bad withholding because payroll systems do not talk to each other.²

Step 2 still needs handling on every W-4 so payroll knows a multiple-job situation exists. Check the box in Step 2(c) if there are exactly two jobs total, or use the Multiple Jobs Worksheet and put the result on Line 4(c) of the highest-paying job’s W-4. Either way, the Line 4b figure goes on one form only.

Step 3 Credits Are a Separate Job

Line 4b lowers the income payroll treats as taxable. Step 3 lowers the tax itself, dollar for dollar. They are not interchangeable, and getting one right while ignoring the other still leaves your withholding off. The Child Tax Credit is $2,200 per qualifying child for 2026, and the Credit for Other Dependents covers qualifying relatives who do not qualify for the CTC.¹² Education credits like the American Opportunity Tax Credit go there too.¹³ A perfect Line 4b entry combined with a blank Step 3 will over-withhold you by roughly $4,400 across the year if you have two children.

Estimate Conservatively

Overstating Line 4b is the real hazard. If you owe more than $1,000 at filing time, the IRS charges an underpayment penalty unless your total withholding and estimated payments cover at least 90% of the current year’s tax or 100% of last year’s tax, whichever is smaller. That prior-year safe harbor rises to 110% if last year’s AGI was above $150,000.¹⁴

A separate $500 civil penalty applies to W-4 statements that reduce withholding without a reasonable basis. It is aimed at inflated numbers a taxpayer knows will not hold up, not honest estimating errors.¹⁵ If you think charitable giving will be somewhere between $8,000 and $12,000, use $8,000. You can file a fresh W-4 later if the actual number climbs.

The IRS Estimator Does the Same Math Online

The IRS Tax Withholding Estimator at irs.gov runs the same calculation with more precision than the paper worksheet. It accounts for income already earned, withholding already taken, and expected deductions and credits, then tells you what to put on Lines 3, 4(a), 4(b), and 4(c).¹⁶ It is especially useful mid-year, when actual pay stubs beat projections and the paper worksheet cannot account for withholding from a job you left.

Turning the Form In and Updating It

Give the completed W-4 to your employer’s payroll or HR department. The form never goes to the IRS. Your employer must start using the new instructions no later than the first payroll period ending on or after 30 days from receipt.¹⁷ Check your first pay stub after that window. If net pay did not rise when you entered a positive Line 4b, follow up with payroll before another pay period runs.

Submit a new W-4 whenever the math changes: a home purchase, marriage, divorce, a child, a side business, or a large charitable gift you had not planned. An annual review each January is worth the ten minutes, because the standard deduction and contribution limits shift every year.

1
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill
2
Internal Revenue Service. Form W-4 (2026) – Employee’s Withholding Certificate
3
Internal Revenue Service. How to Update Withholding to Account for Tax Law Changes for 2025
4
Internal Revenue Service. Publication 936 (2025), Home Mortgage Interest Deduction
5
Internal Revenue Service. Instructions for Schedule A (Form 1040)
6
Internal Revenue Service. Topic No. 502, Medical and Dental Expenses
7
Internal Revenue Service. Expanded Availability of Health Savings Accounts Under the One, Big, Beautiful Bill Act
8
Internal Revenue Service. Retirement Topics – IRA Contribution Limits
9
Internal Revenue Service. Topic No. 456, Student Loan Interest Deduction
10
Internal Revenue Service. Topic No. 458, Educator Expense Deduction
11
Internal Revenue Service. Topic No. 452, Alimony and Separate Maintenance
12
Internal Revenue Service. Understanding the Credit for Other Dependents
13
Internal Revenue Service. American Opportunity Tax Credit
14
Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty
15
Office of the Law Revision Counsel. 26 USC 6682 – False Information With Respect to Withholding
16
Internal Revenue Service. IRS Tax Withholding Estimator Helps Taxpayers Get Their Federal Withholding Right
17
Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide