Yes, a traditional 401(k) contribution comes out of your paycheck before federal income tax is calculated, and in most states before state income tax as well. It does not come out before Social Security and Medicare tax. A Roth 401(k) contribution is the opposite: it comes out after all taxes have already been figured on your full paycheck. Which type you choose changes your take-home pay today and what you owe when you pull the money out later.
What “Pre-Tax” Actually Means on Your Paycheck
When you enroll in a traditional 401(k), your employer subtracts your contribution from your gross pay before running the income tax withholding calculation. The IRS only sees the reduced number for that paycheck. If you earn $2,000 per pay period and contribute $200, federal income tax is calculated on $1,800, not $2,000. The full $200 lands in your retirement account without being trimmed by current income tax.
Your pay stub shows this as two different figures. Gross wages is what you earned. Taxable wages, for federal income tax purposes, is what’s left after the 401(k) deduction. The gap between the two is your contribution.
State income tax usually follows the same rule, but not always. A handful of states tax 401(k) contributions in the year you make them, so your state taxable wages will be higher than your federal taxable wages on the same pay stub even though the same dollars were deducted.
The FICA Exception
Social Security and Medicare taxes do not get the pre-tax treatment. The 6.2% Social Security tax and the 1.45% Medicare tax both apply to your full gross pay, whether or not you contribute to a 401(k).1Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates In the $2,000 paycheck example, FICA is calculated on the whole $2,000 even though income tax is only calculated on $1,800.
There is an upside to this. Because Social Security tax is charged on your full wages, your 401(k) contributions do not reduce the earnings that count toward your future Social Security benefit. Social Security tax applies to earnings up to a wage base of $184,500 in 2026; Medicare tax has no cap.2Social Security Administration. Contribution and Benefit Base
Roth 401(k) Contributions Come Out After Taxes
Roth 401(k) contributions take the reverse path. Your employer calculates all income taxes on your full gross earnings first, then deducts the Roth contribution from what’s left. Your current taxable income is not reduced. A $200 Roth contribution and a $200 traditional contribution pull the same $200 out of your check, but the Roth version leaves you with a smaller take-home amount because you already paid income tax on that $200.
The trade comes at retirement. Qualified withdrawals from a Roth 401(k), including all the investment earnings the account produced, are completely free of federal income tax. To be qualified, the distribution has to happen at least five years after the tax year of your first Roth contribution to the account, and it has to happen after you reach age 59½, become disabled, or die.3Internal Revenue Service. Retirement Topics – Designated Roth Account Pull the money out before meeting both conditions and the earnings portion becomes taxable, with a possible 10% early distribution penalty on top.
Employer Matching Is Always Pre-Tax
One boundary worth knowing: even if every dollar you contribute goes into the Roth side, your employer’s match still goes in on a pre-tax basis. It sits in a separate pre-tax account within the plan, and when you eventually withdraw the matching funds they are taxed as ordinary income.4Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts So a Roth-only contributor still ends up with a taxable bucket inside the same 401(k).
What the Pre-Tax Break Costs You Later
Skipping income tax on the way in means paying it on the way out. Traditional 401(k) withdrawals are treated as ordinary income in the year you take them, and the entire distribution counts, both your original contributions and every dollar of investment earnings. The withdrawal stacks on top of your other income for the year and is taxed at your marginal rate, which runs from 10% to 37% for 2026.5Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
Withdrawals taken before age 59½ generally carry an additional 10% early distribution tax on top of the regular income tax.6Office of the Law Revision Counsel. 26 USC 72 – Annuities, Certain Proceeds of Endowment and Life Insurance Contracts The IRS recognizes a set of exceptions, including leaving your job in or after the year you turn 55, permanent disability, unreimbursed medical expenses above 7.5% of adjusted gross income, and distributions made under a qualified domestic relations order.7Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions The exception waives the 10% penalty but not the underlying income tax.
You also cannot leave a traditional 401(k) untouched forever. Starting at age 73, required minimum distributions kick in, and each one is taxed as ordinary income in the year it is paid out.8Internal Revenue Service. Retirement Plan and IRA Required Minimum Distributions FAQs Under SECURE 2.0, the starting age rises to 75 for people who turn 73 on or after January 1, 2033. Miss an RMD and you owe a 25% excise tax on the amount you should have withdrawn, dropping to 10% if you correct the shortfall within two years.
Choosing Between Pre-Tax and Roth
The mechanical answer to whether a 401(k) comes out before taxes depends entirely on which type you elected when you enrolled. Traditional means lower taxes now and a tax bill later; Roth means paying tax now and taking qualified withdrawals tax-free later. Your plan’s enrollment portal will show the current split, and you can usually change the allocation for future paychecks without affecting what you have already contributed. The combined total of your traditional and Roth deferrals is capped at $24,500 for 2026 across all 401(k) plans you participate in.9Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500