Pre-tax 401(k) contributions are not included in MAGI for any common federal tax calculation. The dollars you defer into a traditional 401(k) are excluded from your W-2 wages before your return is even filed, and no MAGI formula the IRS uses adds them back. Roth 401(k) contributions are the opposite: they’re made with after-tax dollars, stay in your reported wages, and don’t move your MAGI at all. So the short answer to whether 401(k) contributions are included in MAGI depends entirely on which type you’re making.
Why Pre-Tax 401(k) Money Never Shows Up in MAGI
Traditional 401(k) deferrals don’t work like an itemized deduction or an above-the-line adjustment on Schedule 1. Your employer removes the contribution from your gross wages before issuing your W-2. Box 1 already reflects the lower figure. The money never appears as income on your Form 1040, so there’s nothing to subtract later.
Earn $100,000 and defer $24,500 into a traditional 401(k), and your W-2 shows $75,500 in Box 1. That lower number flows straight into your AGI, and from there into every MAGI formula the IRS uses.
This mechanism matters because MAGI calculations work by adding certain items back to AGI. Since your 401(k) contribution was never part of AGI to begin with, there is nothing for a MAGI formula to add back. Compare this to the foreign earned income exclusion or tax-exempt municipal bond interest, which do get added back under several MAGI definitions.1Internal Revenue Service. Modified Adjusted Gross Income (MAGI)
Roth 401(k) contributions are already taxed when they go in, so they remain in your W-2 wages.2Internal Revenue Service. Roth Comparison Chart If your goal is to lower a MAGI figure, only the traditional (pre-tax) side of the plan does the work.
MAGI Isn’t One Number
Modified Adjusted Gross Income starts with AGI and adds back a specific list of items. That list changes depending on which tax provision is asking. The MAGI that governs Roth IRA eligibility is not the same as the MAGI that determines Medicare premiums, which is not the same as the MAGI for the Net Investment Income Tax. There is no universal MAGI figure on your return.
What’s consistent across every version: none of them add back traditional 401(k) contributions. So whichever MAGI you care about, pre-tax deferrals reduce it.
Where a Lower MAGI Actually Helps You
Roth IRA Contribution Eligibility
Direct Roth IRA contributions phase out at higher incomes. For 2026, the range is $153,000 to $168,000 for single filers and $242,000 to $252,000 for married couples filing jointly.3Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 A single filer earning $175,000 who maxes a traditional 401(k) at $24,500 drops MAGI to roughly $150,500, below the phase-out entirely.
Traditional IRA Deduction
If you’re covered by a workplace plan, your ability to deduct a traditional IRA contribution depends on MAGI. For 2026, single filers with a workplace plan lose the deduction entirely above $91,000; joint filers above $149,000. A large 401(k) deferral can pull you back under the threshold, meaning the same contribution earns you tax deferral on the 401(k) side and unlocks a deduction on the IRA side.
ACA Premium Tax Credits
The premium tax credit uses a household income figure that adds tax-exempt interest and foreign earned income to AGI. Pre-tax 401(k) contributions are not added back, so they reduce the income used to size your subsidy. This matters most for self-employed workers and early retirees who can time income to stay under the applicable threshold.
Net Investment Income Tax
The 3.8% NIIT applies when MAGI exceeds $200,000 (single) or $250,000 (joint).4Internal Revenue Service. Topic No. 559, Net Investment Income Tax The MAGI here is AGI plus the foreign earned income exclusion, nothing else.5Internal Revenue Service. Questions and Answers on the Net Investment Income Tax These thresholds are set by statute and don’t adjust for inflation, so 401(k) deferrals are one of the few levers left for reducing exposure.
Medicare IRMAA Surcharges
Medicare’s Income-Related Monthly Adjustment Amount adds to Part B and Part D premiums when MAGI crosses set thresholds. The IRMAA MAGI is AGI plus tax-exempt interest.6Social Security Administration. HI 01101.010 – Modified Adjusted Gross Income (MAGI) For 2026, individuals with MAGI at or below $109,000 (or $218,000 joint) pay no surcharge, and surcharges climb sharply above that.7CMS. 2026 Medicare Parts A and B Premiums and Deductibles
There’s a timing wrinkle worth knowing. IRMAA uses your tax return from two years prior, so 2026 premiums are based on 2024 income. Someone in their early sixties still working can use pre-tax 401(k) contributions in their final working years to keep MAGI below a threshold that would otherwise trigger surcharges once Medicare starts.
Social Security Benefit Taxability
Whether your Social Security benefits are taxable depends on “combined income,” which is AGI (excluding Social Security) plus tax-exempt interest plus half of your benefits.8Internal Revenue Service. Publication 915 (2025), Social Security and Equivalent Railroad Retirement Benefits The base amounts, $25,000 single and $32,000 joint, haven’t been adjusted since 1984. Pre-tax 401(k) contributions reduce the AGI component and can keep benefits partially or fully untaxed, which matters for anyone working part-time while collecting.
How Much MAGI You Can Shave Off in 2026
Your maximum MAGI reduction from a 401(k) equals your elective deferral for the year. For 2026:
- Under age 50: $24,500
- Age 50 and older: $32,500 (includes an $8,000 catch-up)
- Ages 60 through 63: $35,750 (includes an $11,250 enhanced catch-up under SECURE 2.0)
These figures are the employee’s deferral only.3Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Employer matching contributions are a separate pool. They don’t count against these caps, and they don’t reduce your AGI or MAGI either, because they were never part of your wages to begin with.
Consider a 61-year-old single filer earning $220,000. Contributing the full $35,750 pulls AGI down to roughly $184,250. That single move puts them below the $200,000 NIIT threshold, keeps IRMAA at the lowest tier, and holds Roth IRA eligibility intact.
What Happens If You Miscalculate MAGI
Because 401(k) deferrals reduce MAGI so effectively, some people cut it too close and misjudge where they’ll land. If you contribute to a Roth IRA and your final MAGI turns out to be above the phase-out, the excess contribution is hit with a 6% excise tax for every year it stays in the account.9Internal Revenue Service. Retirement Topics – IRA Contribution Limits The penalty stacks year over year until it’s fixed.
You can avoid the penalty by withdrawing the excess and any earnings on it before your tax filing deadline, including extensions.10Internal Revenue Service. IRA Year-End Reminders The withdrawn earnings are taxable in the year the contribution was made. Miss the deadline and you either pay the 6% each year or apply the excess against a future year’s limit once your MAGI drops.
The situation usually arises when someone contributes early in the year based on projected income, then gets an unexpected bonus or capital gain that pushes them over. Leaving a buffer between projected MAGI and the phase-out, or waiting until after you file to make the Roth IRA contribution, prevents it.