Your 401(k) contributions don’t get their own line on Form 1040. Whether they were Traditional (pre-tax) or Roth, your employer has already handled the tax treatment on your W-2, and you simply carry the Box 1 wage figure to Form 1040, Line 1a.1Internal Revenue Service. Form 1040 U.S. Individual Income Tax Return There is no separate deduction, no adjustment on Schedule 1, and no itemized entry on Schedule A. The one place a 401(k) can create an additional entry on the 1040 is the Saver’s Credit, which flows in through Schedule 3.
Why Your W-2 Does the Work
Box 1 of your W-2 (Wages, Tips, Other Compensation) is your taxable federal wage figure after pre-tax 401(k) deferrals have been removed. That is why Box 1 is often smaller than your gross salary. Boxes 3 and 5 (Social Security Wages and Medicare Wages) still include those deferrals, because 401(k) contributions remain subject to FICA even though they escape federal income tax.2Internal Revenue Service. Topic No. 424, 401(k) Plans If the gap between Box 1 and Box 5 roughly matches what you deferred for the year, the payroll side was handled correctly.
Box 12 itemizes the deferral amount using letter codes. For 401(k) plans the two you’ll see are:
- Code D for pre-tax (Traditional) elective deferrals, including any catch-up amount if you’re 50 or older.
- Code AA for designated Roth contributions, including Roth catch-up amounts.
The IRS instructs employers to roll catch-up contributions into the same Code D or Code AA figure rather than breaking them out separately.3Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3 – Section: Box 12 Codes If you made both pre-tax and Roth deferrals in the same year, both codes appear, each with its own amount.
Employer matching contributions do not appear on your W-2 at all. The match goes straight into the plan, is never part of your taxable wages, and never shows up on your 1040.
Pre-Tax (Traditional) 401(k) Contributions
For a Traditional 401(k), there is literally nothing extra to enter. Your employer already subtracted the deferrals before printing Box 1, so by the time you transcribe that number to Line 1a, the tax benefit has already been applied.2Internal Revenue Service. Topic No. 424, 401(k) Plans Trying to deduct the Code D amount again, either on Schedule 1 or Schedule A, would double-count the contribution, and the IRS can see the discrepancy because Box 1 and Box 12 are both reported to them.
Tax software reads the Code D figure when you enter your W-2, but it uses that number only for informational checks like confirming you stayed under the annual deferral limit. It does not generate a deduction. Paper filers can safely leave Code D out of the 1040 math as long as Box 1 lands correctly on Line 1a.
Roth 401(k) Contributions
Roth 401(k) contributions use after-tax dollars, so they are already inside the Box 1 figure. The mechanic on the 1040 is identical: Box 1 to Line 1a, no deduction, no adjustment, no extra form.1Internal Revenue Service. Form 1040 U.S. Individual Income Tax Return The Code AA figure in Box 12 is informational, telling the IRS the money was taxed in the current year so that qualified withdrawals later come out tax-free.
The same handling applies if your plan is required to treat your catch-up contributions as Roth under the SECURE 2.0 rule for employees who earned more than $145,000 in FICA wages the prior year. The catch-up amount shows up under Code AA rather than Code D and sits inside Box 1, but your 1040 entry doesn’t change.4Internal Revenue Service. Treasury, IRS Issue Final Regulations on New Roth Catch-Up Rule, Other SECURE 2.0 Act Provisions
The One Place a 401(k) Creates a Separate 1040 Entry: The Saver’s Credit
Low- and moderate-income taxpayers who contribute to a 401(k) can claim the Retirement Savings Contributions Credit, usually called the Saver’s Credit. This is a dollar-for-dollar reduction in tax owed, not a deduction, and both Traditional and Roth 401(k) contributions count toward it.5Internal Revenue Service. Retirement Savings Contributions Credit (Savers Credit)
You must be at least 18, not a full-time student, and not claimed as a dependent on anyone else’s return. The credit applies to up to $2,000 of contributions ($4,000 if married filing jointly), so the maximum credit is $1,000 single or $2,000 joint. The credit rate — 50%, 20%, or 10% — depends on your adjusted gross income from Form 1040, Line 11. For 2026, the credit phases out entirely above $80,500 for joint filers, $60,375 for heads of household, and $40,250 for single filers.6Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
You calculate the credit on Form 8880 (Credit for Qualified Retirement Savings Contributions).7Internal Revenue Service. Form 8880 Credit for Qualified Retirement Savings Contributions The result goes to Schedule 3, Line 4, and the Schedule 3 total on Line 8 then flows to Form 1040, Line 20.8Internal Revenue Service. 2025 Schedule 3 (Form 1040) That is the one place a 401(k) contribution produces a visible 1040 entry beyond Line 1a.
When You Have to Add 401(k) Money Back to Wages
If your combined elective deferrals across all employers exceed the annual limit, the excess (and any earnings on it) must be distributed from the plan by April 15 of the following year.9Internal Revenue Service. 401(k) Plan Fix-It Guide – Elective Deferrals Werent Limited to the Amounts Under IRC Section 402(g) Miss that deadline and the excess is taxed twice: once in the year of the deferral and again when it eventually comes out.
When a timely correction is made, the excess must be included in wages for the year of the deferral. If your W-2 Box 1 did not already include it (which is how pre-tax excess deferrals arrive), you add the excess to the amount you enter on Line 1a. The plan issues Form 1099-R for the corrective distribution, generally using Code 8 or Code P in Box 7 to flag it as a return of excess deferrals; any earnings paid out with it are taxable in the year you receive them.10Internal Revenue Service. Instructions for Forms 1099-R and 5498
This usually hits people who changed jobs during the year and contributed to two separate 401(k) plans. Neither employer sees what you did at the other, so catching the overage and asking the plan for a corrective distribution before April 15 is on you.