Yes, a 401(k) can reduce your taxable income, but only if you make traditional (pre-tax) contributions. Every dollar you put into a traditional 401(k) comes out of your paycheck before federal income tax is calculated, so it never shows up as taxable wages. Roth 401(k) contributions do not reduce your taxable income, because they are taken from your pay after tax. The 2026 limit on employee contributions is $24,500, which sets the ceiling on how much you can shelter this way.1Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
How a Traditional 401(k) Lowers Your Tax Bill
Your employer treats traditional 401(k) contributions as deferred compensation. The money is pulled from your paycheck before federal income tax is calculated, and the IRS does not count it as current-year wages on your tax return.2Internal Revenue Service. 401(k) Plan Overview Earn $75,000, contribute $10,000, and only $65,000 is taxable wages for federal income tax purposes.
That reduction also lowers your adjusted gross income. A lower AGI can help you qualify for other income-tested tax benefits, such as education credits and deductions that phase out at higher income levels. Inside the account, investments grow without triggering annual capital gains taxes.
The break is a deferral, not a permanent escape. Every dollar you eventually withdraw in retirement is taxed as ordinary income at whatever rate applies that year.2Internal Revenue Service. 401(k) Plan Overview Withdrawals before age 59½ generally trigger an additional 10 percent early withdrawal tax on top of regular income tax.3Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions
Why Roth 401(k) Contributions Don’t Reduce Taxable Income
Roth 401(k) contributions run the other direction. Your employer withholds income tax first, then routes the after-tax money into your Roth account. Because you have already been taxed on those dollars, they stay in your gross income for the year and your tax bill looks the same as if you had not contributed.4Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts
The payoff comes later. Qualified withdrawals from a Roth 401(k), including all investment earnings, are generally tax-free once you are past age 59½ and at least five tax years have passed since your first Roth contribution to the plan.4Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts So the choice is upfront tax relief now (traditional) versus tax-free income later (Roth).
What 401(k) Contributions Do Not Reduce: Social Security and Medicare Taxes
Even a traditional 401(k) contribution does not cut your Social Security or Medicare (FICA) taxes. The IRS specifically requires elective deferrals, whether traditional or Roth, to be included in wages subject to Social Security, Medicare, and federal unemployment taxes.2Internal Revenue Service. 401(k) Plan Overview Earn $75,000 and defer $10,000: income tax applies to $65,000, but FICA still applies to the full $75,000.
You will see Social Security (6.2 percent) and Medicare (1.45 percent) withheld on your entire salary regardless of how much you contribute. Your future Social Security benefit calculation is unaffected by 401(k) contributions, because your full earnings are still credited toward the benefit formula.
How Much You Can Shelter in 2026
The IRS caps how much taxable income you can defer each year. For 2026, the standard employee deferral limit is $24,500.1Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 That limit is combined across traditional and Roth contributions, so you cannot put $24,500 into each.
Older workers get more room. If you are 50 or older, you can add $8,000 in catch-up contributions for a total of $32,500. Under SECURE 2.0, workers aged 60 through 63 get a higher catch-up of $11,250, bringing their maximum employee contribution to $35,750 for 2026.1Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Only the traditional portion of what you contribute actually reduces your taxable income.
Confirming the Reduction on Your W-2
Your employer reports 401(k) deferrals in Box 12 of Form W-2 using Code D for traditional contributions and Code AA for Roth contributions.5Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3 To check that the tax reduction was applied, look at Box 1, which shows your taxable wages.
If you made traditional contributions, Box 1 should be lower than your total salary by roughly the amount in Box 12 Code D. The Box 1 figure is what flows onto your tax return; payroll has already subtracted the pre-tax deferral. Contribute only to a Roth 401(k) and Box 1 will match your full salary, because after-tax contributions are not excluded.
A Bonus for Lower Earners: The Saver’s Credit
Contributing to a 401(k), traditional or Roth, may also qualify you for the Retirement Savings Contributions Credit, known as the Saver’s Credit. This is a direct tax credit, not just a deduction, worth up to $1,000 for single filers or $2,000 for married couples filing jointly.6Internal Revenue Service. Retirement Savings Contributions Credit (Saver’s Credit)
To qualify for 2026, your AGI must fall at or below:
- $80,500 for married filing jointly
- $60,375 for head of household
- $40,250 for single or married filing separately
The credit rate is 50 percent, 20 percent, or 10 percent of your contribution depending on income and filing status, with lower earners getting the highest rate.1Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Traditional 401(k) contributions can produce a stacked benefit here: the contribution itself reduces your AGI, which may push you into a higher credit rate bracket.