Roth 401(k) vs. Traditional 401(k): 2026 Decision Guide for High Earners
Both go into the same payroll slot. The difference is when you pay taxes — now (Roth) or later (Traditional). For high earners at $1M–$5M, the decision usually leans Roth: no income cap, no mandatory lifetime RMDs, and distributions that are invisible to Medicare IRMAA surcharges. But the math depends on your specific rate now vs. in retirement.
The core math
Roth 401(k) and traditional 401(k) contributions grow at the same rate — both are sheltered from dividends, interest, and capital gains tax while inside the account. The only difference is the tax treatment at the two endpoints:
- Traditional 401(k): Contributions reduce your taxable income now (pre-tax), and you pay ordinary income tax on every dollar withdrawn in retirement.
- Roth 401(k): Contributions get no current deduction (after-tax), but every withdrawal in retirement is completely tax-free — principal and growth alike.
The clean result: if your tax rate is identical now and in retirement, both strategies produce the same after-tax wealth — assuming you invest any tax savings from the traditional deduction at the same rate and pay capital gains tax on the gains. Roth wins when your retirement rate will be higher; Traditional wins when it will be lower.
The real question for this audience: will your retirement rate actually be lower? For most $1M–$5M investors, the honest answer is no — and often it rises.
| Your situation | Likely winner | Why |
|---|---|---|
| High earner now; similar income from RMDs + SS in retirement | Roth 401(k) | Rate parity or increase; RMD compounding and IRMAA savings add up |
| Peak earnings now; expect dramatic income drop at retirement | Traditional | Pay 35–37% now vs. 22% later — meaningful savings |
| Plan to relocate from CA / NY / NJ to TX / FL before retirement | Traditional | Defer at combined 40–50% rate; withdraw in a 0% state |
| Large existing pre-tax balance; high projected RMDs | Roth 401(k) | Builds tax-free bucket; reduces future forced distributions |
| Age 50+ with $150K+ FICA wages from your employer in 2025 | Roth (required) | SECURE 2.0 § 603 catch-up mandate applies starting 2026 |
4 reasons high earners lean toward Roth 401(k)
1. No income limit — unlike the Roth IRA
Direct Roth IRA contributions phase out between $153,000 and $168,000 (single) and $242,000 and $252,000 (MFJ) in 2026 — this audience is typically phased out entirely.1 The backdoor Roth IRA workaround moves up to $7,500 per year. A Roth 401(k) contribution moves up to $24,500 — with no income limit whatsoever. Every participant in a plan that offers a Roth 401(k) option can elect Roth contributions regardless of income.
2. No lifetime required minimum distributions
SECURE 2.0 Act § 325 eliminated mandatory lifetime RMDs for Roth 401(k) and Roth 403(b) accounts, effective starting in 2024.3 Traditional 401(k) and traditional IRA accounts still trigger RMDs beginning at age 73 (born 1951–1959) or age 75 (born 1960+). For a $1M–$5M investor with large pre-tax balances, those forced distributions commonly push MAGI into the 32%–35% bracket — on top of Social Security income, investment income, and any pension.
Practical impact: a traditional 401(k) balance of $800,000 growing at 7% for 20 years reaches ~$3.1M. At age 75 with a Uniform Lifetime Table divisor of 24.6, the first-year RMD is roughly $126,000. Add $40,000 of Social Security (85% includible), and a married couple's taxable income starts near $167,000 — already in the 22% bracket without any other income. A Roth 401(k) balance requires no withdrawal — ever — unless the account owner chooses to take it.
3. Roth distributions are invisible to Medicare IRMAA
Medicare Part B and Part D surcharges (IRMAA) are based on your modified adjusted gross income from two years prior. In 2026, the first IRMAA tier begins above $109,000 (single) / $218,000 (MFJ), adding $974/year per person in Medicare costs. Traditional 401(k) and IRA withdrawals count as ordinary income — fully included in MAGI. Roth 401(k) qualified distributions do not — they are excluded from gross income entirely.4
A couple taking $60,000/year in retirement distributions keeps $60,000 off their Medicare MAGI every year for life if those distributions come from Roth instead of Traditional. Over a 20-year retirement, even staying in the first IRMAA tier, that's roughly $19,480 in avoided Medicare surcharges (couple basis). A large RMD that crosses a higher tier costs far more.
4. The Roth catch-up mandate (starting 2026)
Under SECURE 2.0 § 603, plan participants age 50 or older who earned more than $150,000 in FICA wages from the same employer in the prior calendar year must make any catch-up contributions as designated Roth contributions — no choice — starting in 2026.5 If you earned $150K+ from your employer in 2025 and are 50 or older, your catch-up dollars go Roth this year. This applies to the $11,250 super catch-up for ages 60–63 as well. The threshold is indexed for inflation in future years.
2026 contribution limits
| Age group | Standard deferral | Catch-up | Total deferral |
|---|---|---|---|
| Under 50 | $24,500 | — | $24,500 |
| 50–59 and 64+ | $24,500 | $8,000 | $32,500 |
| 60–63 (super catch-up) | $24,500 | $11,250 | $35,750 |
Source: IRS Notice 2025-67.2 The same dollar limits apply to both Roth 401(k) and traditional 401(k) contributions. Total employer + employee contributions (all sources) cannot exceed the § 415(c) limit: $72,000 (under 50), $80,000 (age 50–59 / 64+), $83,250 (ages 60–63).
Roth 401(k) vs. Traditional 401(k) Calculator — 2026
Enter your annual contribution, current marginal rate, and your expected retirement tax rate to see which strategy leaves you with more after-tax wealth.
Uses the future value of an annuity formula (same annual contribution each year). Does not model the Traditional 401(k) tax savings reinvested in a taxable account, state income tax, IRMAA savings, or the no-RMD compounding benefit of Roth 401(k) — all of which favor Roth for this audience and are not reflected in these numbers. Federal tax only.
When Traditional 401(k) still wins
- You're at peak earnings and expect a genuine income drop at retirement. If you're solidly in the 35%–37% bracket now and genuinely expect to live on Social Security and modest distributions at the 22% rate in retirement, the deduction today is worth more. This is rarer than people assume — RMDs and taxable portfolio income close the gap.
- You plan to relocate to a no-income-tax state before distributions begin. California (13.3% top marginal rate), New York (10.9%), and New Jersey (10.75%) residents who retire in Texas, Florida, or Nevada can defer state income tax entirely on traditional contributions. Combined marginal rates of 40–50% today vs. 22% federal-only at withdrawal is a compelling spread — but requires actually making the move and keeping the new domicile clean from the old state's residency rules.
- Your heirs are in low brackets. If your primary beneficiaries earn $40,000/year and would inherit a traditional IRA distributed over 10 years at the 12%–22% rate, their tax cost may be lower than what you'd pay now at 35%+ to contribute Roth. Requires modeling both paths — worth doing before assuming Roth is automatically better for estate planning.
- Your plan doesn't offer a Roth 401(k). Some employer plans — particularly smaller ones — haven't added the Roth option. If traditional-only is available, use it, and supplement with a backdoor Roth IRA ($7,500/yr) plus Roth conversions in lower-income years to build the tax-free bucket separately.
The split approach
You don't have to pick one or the other. A split strategy contributes enough to the traditional 401(k) to fill your current bracket to its top, then routes additional dollars to the Roth 401(k). Example: a married couple with $240,000 in gross income is in the 22% bracket (taxable income ~$207,800 after the $32,200 standard deduction). They can defer ~$3,600 of additional traditional contributions to push taxable income to the 22% bracket top at $211,400 — capturing that deduction at 22% — then put any remaining catch-up room into the Roth 401(k). This is essentially the same logic as Roth conversion planning: fill the current bracket, then Roth the rest.
Get matched with a fee-only advisor for 401(k) optimization
A fee-only advisor specializing in $1M–$5M clients can project your current vs. retirement tax rates, model your RMD trajectory, and tell you whether Roth 401(k), traditional, or a bracket-filling split strategy maximizes your lifetime after-tax wealth.
Sources
- IRS Notice 2025-67 — 2026 Roth IRA phaseout: $153,000–$168,000 (single); $242,000–$252,000 (married filing jointly): irs.gov.
- IRS Notice 2025-67 — 2026 401(k) elective deferral limit $24,500; catch-up $8,000 (age 50+); enhanced catch-up $11,250 (ages 60–63); § 415(c) total limits $72,000 / $80,000 / $83,250: irs.gov.
- SECURE 2.0 Act of 2022, § 325 (Public Law 117-328) — eliminates lifetime required minimum distributions for Roth 401(k) and Roth 403(b) accounts for distribution calendar years beginning after December 31, 2023: congress.gov.
- IRC § 86, § 36B — Roth 401(k) qualified distributions are excluded from gross income and therefore excluded from modified adjusted gross income used for Medicare IRMAA determinations. 2026 IRMAA first-tier threshold $109,000 (single) / $218,000 (MFJ) per CMS 2026 Medicare Parts A & B Premiums Fact Sheet: cms.gov.
- SECURE 2.0 Act § 603; IRS Final Regulations (IRB 2025-40) — participants age 50+ with FICA wages exceeding $145,000 (indexed; $150,000 for 2026) from the same employer in the prior calendar year must make catch-up contributions as designated Roth contributions: irs.gov. Threshold is indexed for inflation after 2026. Confirm implementation date with your plan administrator.
Contribution limits verified against IRS Notice 2025-67 (2026). Tax brackets per IRS Rev. Proc. 2025-32 (2026). IRMAA first-tier threshold per CMS 2026 Medicare fact sheet. Roth catch-up mandate per SECURE 2.0 § 603 and IRS Final Regulations (IRB 2025-40). Values current as of June 2026.