401(k) vs Roth 401(k): Taxes and Your Take-Home Pay

Pre-tax 401(k) deferrals reduce current federal income-taxable wages; designated Roth deferrals are taxed now, while qualified withdrawals are tax-free. At equal take-home cost and identical growth, the simplified comparison below favors pre-tax when the later withdrawal tax rate is lower, and Roth when it is higher. Actual choices also depend on withdrawal eligibility, contribution room, other income and plan terms. Both share the 2026 employee deferral ceiling of $24,500, subject to compensation and other applicable limits. If the plan permits catch-up contributions, eligible participants turning 50 or older may add $8,000, or $11,250 instead at ages 60 through 63. These are the IRS 2026 cost-of-living limits.

Quick answer

• Rule of thumb: at equal take-home cost, identical growth and flat tax rates, pre-tax produces more after-tax proceeds if the later rate is lower, Roth if it is higher, and they tie at equal rates. A split can diversify tax treatment, but no universal percentage is optimal.
• One limit, not two: $24,500 in 2026 generally covers combined pre-tax and Roth 401(k)/403(b) elective deferrals across employers. A 457(b) plan has a separate limit; compensation, plan terms and other applicable limits can reduce the amount you may contribute. Catch-up amounts sit on top: $8,000, or $11,250 at ages 60 to 63 if your plan allows it.
• Equal deposits are not equal cost: at a hypothetical 20% marginal rate, $1,000 deferred pre-tax reduces take-home pay by about $800. The same $1,000 as Roth costs the full $1,000.
• Roth is not automatically tax-free: the IRS treats a designated Roth distribution as qualified only after a five-taxable-year period of participation and after age 59½, death or disability. Miss that and the earnings slice is taxable, pro rata.
• Watch two plan-dependent items: your employer match is pre-tax by default and can only be Roth if the plan permits it and you're fully vested in it. And if your 2025 FICA wages from your employer topped $150,000, your 2026 catch-up has to be Roth.

Same deferral, two different tax bills

A designated Roth account is a separate account inside your 401(k) or 403(b), not a different plan. Same investment menu in almost every case, same recordkeeper, same paycheck election screen. What changes is the tax timing. IRS guidance is blunt about it: designated Roth contributions are not excluded from gross income and are taxed currently, while qualified distributions from the account, earnings included, are excluded from gross income.

Pre-tax deferrals work the other way. The money skips federal income tax withholding on the way in, grows without annual tax drag, and then every dollar of withdrawal lands in your ordinary income for that year. Neither election reduces your Social Security or Medicare payroll taxes.

Neither account generally imposes annual income tax on dividends or gains while the money remains in the plan. Pre-tax growth is tax-deferred, however: taxable withdrawals include earnings. Qualified Roth withdrawals are tax-free. Calling both types of growth tax-free obscures that distinction.

The 2026 numbers that cap what you can put in

These are the figures that actually constrain the decision. All are for 2026, from the IRS cost-of-living page for dollar limitations and the IRS 401(k) plan overview.

Switching employers does not restart the individual 402(g) deferral limit. The IRS multiple-plan guidance distinguishes the separate 457(b) limit. The annual-additions ceiling includes regular deferrals, employee after-tax contributions and employer amounts; it excludes eligible catch-up deferrals and is also limited by compensation. Employer aggregation and special rules can matter when participating in more than one plan, so the $72,000 figure is not an extra employee deferral allowance.

A $1,000 budget, run through three withdrawal rates

Here's the arithmetic, and it's explicitly hypothetical. Assume you have $1,000 of take-home pay you're willing to give up this year, a 20% current marginal income tax rate, one contribution that doubles in value before you withdraw it, and a single withdrawal taxed at one flat rate. The doubling is an assumption for the math, not a forecast. This example excludes investment fees, state and local income taxes, and any employer match.

The Roth side is simple. A $1,000 Roth deferral costs $1,000 of take-home pay because it's made with taxed dollars. It doubles to $2,000, and a qualified withdrawal delivers $2,000.

The pre-tax side needs a gross-up, and this is the step most comparisons skip. To reduce take-home pay by exactly $1,000 at a 20% marginal rate, you defer $1,250: the deferral cuts your taxable wages by $1,250, which trims $250 of tax, so your paycheck falls by $1,000. That $1,250 doubles to $2,500. Then the withdrawal tax applies to the whole balance.

Pre-tax comes out $250 ahead in the 10% scenario, dead even at 20%, and $250 behind at 30%. That symmetry holds under the example's assumptions. When growth is identical and one flat rate hits the entire withdrawal, the result depends only on which rate is higher, today's or the later one, and the deposit's size difference is exactly the tax you prepaid.

Now break the equal-cost rule and watch the answer change dishonestly. Put $1,250 into the Roth account instead, and it grows to $2,500 and delivers $2,500 after a qualified withdrawal, beating pre-tax in every scenario. But that election cost you $1,250 of take-home pay, 25% more than the pre-tax version. You didn't find a better account, you just saved more money.

At the $24,500 deferral ceiling, Roth uses more take-home pay: $24,500 versus $19,600 for pre-tax at the assumed 20% rate. An equal-cost comparison should also track the $4,900 of tax savings available outside the pre-tax account; whether it is saved, and how it is taxed and invested, affects the outcome. Below the ceiling, grossing up a pre-tax contribution requires enough compensation and remaining contribution room, and may be restricted by the Roth catch-up rule. A larger after-tax amount inside a Roth account alone does not prove that the household is better off overall.

What "qualified" means before your Roth money comes out clean

The IRS designated Roth FAQ sets two conditions. The distribution has to come after a five-taxable-year period of participation, which begins on the first day of the taxable year for which you made your first designated Roth contribution to that plan, and it has to be made on or after age 59½, on or after death, or after you become disabled.

Fail either test and you have a nonqualified distribution, taxed pro rata. The IRS uses this example: a $5,000 nonqualified distribution from an account holding $9,400 of contributions and $600 of earnings is treated as $4,700 of contributions, excluded from income, and $300 of earnings, includible, with a possible 10% early distribution tax on that earnings piece. You cannot cherry-pick your contributions out of a designated Roth account the way you can from a Roth IRA. That's the main practical difference between the two Roth wrappers, along with the Roth IRA's income limits, which designated Roth accounts don't have.

Designated Roth accounts have no lifetime required minimum distributions (RMDs) for the owner; beneficiary rules still apply. Pre-tax 401(k) RMD timing depends on birth year and plan/employment circumstances. For example, the IRS final RMD regulations set age 75 for people born in 1960 or later, so age 73 is not universal. A qualifying still-working participant may delay RMDs from the current employer's plan until retirement if the plan allows; the ownership exception excludes employees who are 5% owners under the tax-code definition. The first required distribution generally has an April 1 following-year deadline. Check current rules for the relevant birth cohort rather than applying a single age to every reader.

Your match may not follow your election

Employer matching money is a separate contribution type, and the default treatment is pre-tax even when 100% of your own deferrals are Roth. SECURE 2.0 opened a door here: a plan may let you designate matching or nonelective contributions as Roth, and IRS Notice 2024-2, section L supplies the mechanics. Two conditions matter. You have to be fully vested in that contribution at the time it's allocated, and you have to make the designation before the contribution is made.

Roth match also comes with a tax bill nobody withholds for you. Under Notice 2024-2, designated Roth matching and nonelective contributions are includible in gross income in the year they're allocated, reported on Form 1099-R as an in-plan Roth conversion, and they aren't treated as wages for income tax withholding or subject to FICA or FUTA. So a $4,000 Roth match adds $4,000 to your taxable income with nothing pre-paid, which can turn into an underpayment at filing time.

Vesting is the other reason your match might be off the table for Roth treatment. Your own elective deferrals are always 100% vested, but a plan may require a set number of years of service before you own employer or matching contributions. A three-year cliff schedule means a two-year employee has no fully vested match to designate.

When "just go Roth" is the weaker call

Age alone does not determine the better tax election. The worked example compares specified tax rates and equal take-home cost; actual retirement withdrawals may span tax brackets and interact with other income. Use those assumptions to understand the direction of the trade-off, not to predict an exact personal saving.

Pre-tax may be useful when the current deduction saves tax at a higher rate than later withdrawals will incur, or when lower withholding helps you afford contributions needed for an available match. Evaluate the match formula and vesting before treating it as money you will necessarily keep. A planned move between states is another input, but does not by itself establish the full future tax cost.

Roth may be useful when the current marginal rate is low relative to the expected tax on withdrawals, or when reducing future taxable distributions is valuable. Large pre-tax balances and contribution ceilings also deserve consideration, with the equal-cost caveat above. The IRS catch-up guidance requires Roth treatment for covered 2026 catch-up contributions when 2025 FICA wages from the plan sponsor exceeded $150,000. This does not force all regular deferrals to Roth. Confirm eligibility and the plan's Roth feature with payroll. The IRS final-regulations announcement permits reasonable good-faith implementation before general regulatory applicability in 2027; that does not postpone the statutory 2026 requirement.

Four mistakes that show up in real accounts

1. Believing every Roth withdrawal is tax-free. A distribution before age 59½ is not qualified merely because five taxable years have passed. Death or disability can satisfy the separate qualifying-event condition; otherwise the earnings portion of a nonqualified distribution is generally taxable, with a possible additional tax and applicable exceptions.
2. Ignoring rollover-specific clocks. The IRS designated Roth FAQ says a direct rollover between designated Roth plans can carry the earlier plan's starting year into the receiving plan. A rollover to a Roth IRA instead uses the Roth IRA's own qualification period; time in the employer plan does not establish that IRA period. Confirm the rollover route and account records before counting years.
3. Comparing equal deposits. $500 pre-tax and $500 Roth per paycheck are not the same sacrifice, and any comparison that treats them as equal will flatter the Roth.
4. Never revisiting the election. The right split in a $60,000 year isn't obviously right in a $200,000 year, or in a year with a big bonus, a sabbatical or a job change.

Do this before your next payroll cutoff

Open your plan's summary plan description and find four things: whether a designated Roth deferral option exists, whether the plan permits Roth matching contributions, the match formula, and the vesting schedule for employer money. Then check your year-to-date deferrals against the $24,500 limit before you change anything, because a mid-year switch to Roth doesn't create new room.

If future tax rates are uncertain, splitting contributions is one option, not a universally correct 50/50 prescription. Choose a sustainable total contribution, account for any available match and vesting conditions, and check remaining annual room across jobs. Use the payroll election method your plan supports and revisit it when compensation or circumstances change.