What Do Deductions on a W-4 Mean for Your Withholding?

Deductions on a W-4 are the dollar amount you enter on Step 4(b) of the form to tell your employer that a portion of your pay should not be subject to federal income tax withholding. On the 2026 form, that number comes from a worksheet covering itemized deductions above your standard deduction, above-the-line adjustments like IRA contributions and student loan interest, and four newer categories: qualified tips, overtime premium pay, passenger vehicle loan interest, and a senior bonus deduction.¹ Get the figure right and your paycheck reflects what you’ll actually owe; get it wrong in either direction and you’ll either float the government an interest-free loan or face a bill at filing time.

What Step 4(b) Actually Does

Whatever number you write on Step 4(b), your employer’s payroll system subtracts it from your taxable wages before running the withholding calculation. Higher number, less tax withheld each payday. Lower number, or a blank line, and withholding is based only on your standard deduction for your filing status.¹

That default matters. If you take the standard deduction and don’t have IRA contributions, student loan interest, tips, overtime, auto loan interest, or a senior deduction to claim, you can leave Step 4(b) blank. The payroll system already accounts for the standard deduction on its own. You only need the worksheet when you have something to add on top of it.¹

The point of the exercise is to line up withholding with actual tax liability. Too little withheld can trigger an underpayment penalty. Too much and your refund is really just money you overpaid all year.²

When the Line Is Worth Filling In

Because the standard deduction is baked in automatically, itemized deductions only help your withholding to the extent they exceed it. For 2026 the standard deduction is $16,100 for single filers or married filing separately, $32,200 for married filing jointly or a qualifying surviving spouse, and $24,150 for head of household. Taxpayers 65 or older get an additional $2,050 (single) or $1,650 per qualifying spouse (joint).³

Even if your itemized deductions won’t clear those thresholds, Step 4(b) can still be worth completing. The above-the-line adjustments and the four newer deductions all reduce your withholding independently of whether you itemize.

What Counts as a Deduction on the W-4

Itemized Deductions Above the Standard Deduction

If your itemized deductions will exceed your standard deduction, only the excess feeds into Step 4(b). The categories the worksheet asks you to estimate:

State and local taxes (SALT): property taxes plus either state income taxes or state sales taxes. The 2026 cap is $40,400, or $20,200 if married filing separately, for taxpayers with total income below $505,000 ($252,500 if married filing separately). The cap phases down toward $10,000 at higher incomes.¹
Home mortgage interest on debt up to $750,000, or $375,000 if married filing separately, including mortgage insurance premiums.
Charitable contributions, but only the amount that exceeds 0.5% of your total income on the 2026 worksheet.¹
Medical and dental expenses, but only the portion above 7.5% of your total income.

The worksheet also applies an income-based limitation on the total itemized figure for higher earners before it’s compared with the standard deduction.¹

Above-the-Line Adjustments

These reduce adjusted gross income whether you itemize or not, and they go on line 5 of the worksheet:⁴

Traditional IRA contributions, up to $7,500 for 2026 if you’re under 50 or $8,600 if you’re 50 or older. Income limits and workplace retirement plan coverage can reduce or eliminate the deduction.⁵
Student loan interest, up to $2,500, phasing out between $85,000 and $100,000 in modified adjusted gross income for single filers and $175,000 to $205,000 for joint filers.⁴
Educator expenses, up to $300 for eligible K–12 teachers, counselors, principals, and aides who work at least 900 hours per school year, or $600 if both spouses qualify on a joint return.⁶
Alimony paid under pre-2019 divorce agreements and other Schedule 1 adjustments.

The Four Newer Deductions

The One, Big, Beautiful Bill Act, signed on July 4, 2025, added four deductions that appear on the 2026 worksheet for the first time. Each is temporary, covering tax years 2025 through 2028, and each has its own cap and income phase-out. All four are available whether you itemize or take the standard deduction.⁷

Qualified tips. Up to $25,000 per year if you work in an occupation that customarily receives tips. Phase-out begins at $150,000 modified adjusted gross income, or $300,000 for joint filers. Tips have to be reported on your W-2, a 1099, or Form 4137. Tips in a “specified service trade or business” under the qualified business income rules do not qualify.⁷

Qualified overtime compensation. Up to $12,500 per year, or $25,000 joint, covering the premium portion of overtime pay (the extra half in time-and-a-half). The overtime has to be required under the Fair Labor Standards Act. Same $150,000/$300,000 income phase-out.⁷

Passenger vehicle loan interest. Up to $10,000 per return on interest for a personal-use vehicle whose final assembly is in the United States and where the loan is secured by the vehicle. Lease payments don’t count. Phase-out starts at $100,000 modified adjusted gross income, or $200,000 for joint filers.⁷

Senior deduction. $6,000 per qualifying person age 65 or older, up to $12,000 on a joint return where both spouses qualify. This is separate from the additional standard deduction seniors already receive. It phases out at a 6% rate above $75,000 for single filers and $150,000 for joint filers. It appears on lines 3a and 3b of the worksheet.¹

Walking the 2026 Worksheet

The Deductions Worksheet lives on page 4 of the 2026 W-4 and runs 15 lines. You keep it. Only the final total goes on Step 4(b) of the form your employer sees.¹

Lines 1a–1c: estimated qualified tips, overtime premium, and auto loan interest, each within its cap.
Line 2: sum of 1a–1c.
Lines 3a–3b: $6,000 per qualifying person 65 or older, subject to the income thresholds.
Line 4: sum of 3a and 3b.
Line 5: above-the-line adjustments (IRA, student loan interest, educator expenses, and similar items).
Lines 6a–6e: itemized categories (medical above 7.5% of income, SALT within the cap, mortgage interest, charitable above 0.5% of income, other itemized).
Line 7: total itemized deductions.
Lines 8–10: the income-based limitation on itemized deductions for higher earners.
Lines 11–12: subtract your standard deduction from the limited itemized total. If itemized is smaller, this is zero.
Lines 13–15: add lines 2, 4, 5, and 12. Line 15 is the number for Step 4(b).

Because lines 2, 4, and 5 flow into the total separately from the itemized comparison, the newer deductions and the above-the-line adjustments help even if your itemized total falls below your standard deduction.

If You Have More Than One Job

Complete Steps 3 through 4(b) on only one W-4, the one for your highest-paying job. Leave those steps blank on any other W-4s. Entering deductions on more than one form double-counts them and produces under-withholding.¹

When to Update the Form

You can file a new W-4 with your employer any time. Life events that typically call for one include marriage or divorce, having a child, buying a home, picking up or losing a second job, and retiring.⁸

Some updates aren’t optional. If a change in your circumstances reduces the withholding allowances you’re entitled to claim, say your filing status shifts from married filing jointly to single or you lose eligibility for the child tax credit, you have 10 days to submit a new W-4.⁸

Penalties for Getting It Wrong

If withholding falls too far short of what you owe, the IRS can charge an underpayment penalty. You generally avoid it if you owe less than $1,000 after withholding and credits, or if you paid at least 90% of the current year’s tax or 100% of last year’s, whichever is smaller. If your prior-year adjusted gross income was above $150,000, the safe harbor rises to 110% of last year’s tax.⁹

Inflating deductions on the W-4 to shrink withholding carries a separate $500 civil penalty when there was no reasonable basis for the information provided. That penalty is on top of taxes and interest owed. The IRS may waive it if credits and estimated payments end up covering your full tax liability.¹⁰

1
IRS. Form W-4, 2026 Employee’s Withholding Certificate
2
Internal Revenue Service. About Form W-4, Employee’s Withholding Certificate
3
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
4
Office of the Law Revision Counsel. 26 USC 62 – Adjusted Gross Income Defined
5
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
6
Internal Revenue Service. Topic No. 458, Educator Expense Deduction
7
Internal Revenue Service. One, Big, Beautiful Bill Provisions – Individuals and Workers
8
Internal Revenue Service. Publication 505, Tax Withholding and Estimated Tax
9
Office of the Law Revision Counsel. 26 USC 6654 – Failure by Individual to Pay Estimated Income Tax
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Office of the Law Revision Counsel. 26 USC 6682 – False Information With Respect to Withholding