401(k) vs Roth IRA Optimizer

Same pre-tax salary committed to retirement saving. Which path produces a larger after-tax nest egg: a traditional pre-tax 401(k) or a post-tax Roth IRA? The answer depends almost entirely on whether your retirement marginal rate will be higher or lower than your current rate.

Last reviewed Apr 27, 2026 · SN

For information only — not investment, financial, or tax advice. This calculator estimates results based on the inputs you provide. It does not constitute professional advice and infoz.com is not a CPA, EA, attorney, or registered investment adviser. Tax laws change. Individual circumstances vary. Consult a qualified professional licensed in your jurisdiction before making any financial decision.

Recommendation

Traditional 401(k) wins

30 years until retirement · marginal rate delta 2.0%

Traditional 401(k)

$2,173,705

After-tax retirement value

Pre-tax contribution: $23,500/yr
Employer match: $11,750/yr
FV (gross, pre-tax): $2,786,801

Roth IRA

$2,136,547

After-tax retirement value

Post-tax contribution: $17,860/yr
Employer match (still 401k): $11,750/yr
FV Roth (tax-free): $1,411,979

Always capture the full employer match first. Employer 401(k) matches are pre-tax dollars from your employer — declining them is leaving cash on the table regardless of which strategy you pick afterward.

How this calculator works

Both paths grow at the same real return; the difference is when tax is paid. The calculator computes after-tax future value of each path for the same pre-tax dollar commitment.

Compute employer match
match = preTaxContribution × matchPct. Always added to the 401(k) on both paths since employer matches are pre-tax regardless.
Traditional path
FV(preTax + match) growing at r for n years; multiply by (1 − retirementMarginalRate) for after-tax value.
Roth path
Effective contribution = preTax × (1 − currentMarginalRate). FV grows tax-free; no tax on withdrawal. Add the matched 401(k) FV taxed at retirement rate.
Compare
Higher after-tax FV wins. If within $1 of each other, the calculator reports a tie.

Trad after-tax = (PMT_pre + match) × ((1+r)^n − 1)/r × (1 − retRate) Roth after-tax = PMT_pre × (1 − currRate) × ((1+r)^n − 1)/r + match × ((1+r)^n − 1)/r × (1 − retRate)

Worked example: Age 35 → 65, $23,500 pre-tax, current rate 32%, retirement rate 12%, 6% real, 50% match

n = 30 years; r = 6%; match = 23,500 × 50% = $11,750. Traditional path: Annual growing = 23,500 + 11,750 = 35,250 FV gross ≈ 35,250 × ((1.06)^30 − 1)/0.06 ≈ 35,250 × 79.058 ≈ 2,786,000 After tax (× 0.88) ≈ $2,452,000 Roth path: Roth annual = 23,500 × (1 − 0.32) = $15,980 FV Roth ≈ 15,980 × 79.058 ≈ $1,263,000 (tax-free) Match still 401k → FV match × 0.88 ≈ 11,750 × 79.058 × 0.88 ≈ $817,000 Total Roth after-tax ≈ $2,080,000 Verdict: Traditional wins by ~$370k. Reason: dropping from 32% current rate to 12% retirement rate is the dominant factor when the rate spread is wide.

Sources & methodology

Every numeric input to this calculator traces back to one of the following authoritative documents.

IRS — Retirement Topics: Contributionsprimary · accessed 2026-04-27
IRS — IRA contribution limitsprimary · accessed 2026-04-27
Investor.gov — Traditional vs. Rothsecondary · accessed 2026-04-27

Frequently asked questions

Why does the optimizer focus on marginal tax rates?: Because pre-tax-vs-post-tax retirement contribution math collapses to: which marginal rate is higher — now or in retirement? If now > retirement, traditional wins. If retirement > now, Roth wins. If equal, they're a tie (assuming the same return path and contribution limits). Real life adds complications (RMDs, state taxes, Social Security taxation), but the marginal rate is the dominant lever.
What about the employer match?: Employer 401(k) matches are always pre-tax — they go into a traditional 401(k) regardless of whether you contribute to a Roth. The calculator includes the match on both sides, which is why declining the match is never sensible. Always capture the full match before deciding pre-tax vs. Roth for the rest.
Are contribution limits checked?: No. The calculator runs whatever annual contribution you enter. Real IRS limits for 2026 are roughly $24,500 employee 401(k) and $7,500 IRA (placeholders pending final IRS notice). Roth IRA also has an income phase-out — high earners are blocked from direct Roth contributions and may need a backdoor Roth instead. The optimizer ignores these.
What about RMDs?: Required Minimum Distributions kick in at age 73 (or 75, depending on birth year per the SECURE 2.0 Act) and force traditional 401(k) / IRA balances to be drawn down on a schedule, possibly at higher tax rates. Roth accounts have no RMDs. The calculator does not model this; in practice it favors Roth somewhat at very high balances.
Is this advice?: No. For advice on your specific situation, talk to a fiduciary fee-only financial planner — and consider that pre-tax vs Roth is one of the highest-leverage decisions in retirement planning, so it pays to get it right.

Important disclaimers

No professional advice. This calculator is provided for informational and educational purposes only and does not constitute investment, financial, or tax advice. infoz.com is operated by Netlink BVI Ltd, which is not a certified public accountant, enrolled agent, attorney, registered investment adviser, or licensed financial professional in any jurisdiction. Use of this calculator does not create any professional, fiduciary, or advisory relationship.

No warranties. Results are best-effort estimates based on the inputs you provide and the data sources cited. Tax law and financial regulations change without notice; data may be revised, withdrawn, or superseded between releases. We make no warranty, express or implied, that the result is accurate, current, complete, or suitable for your situation.

No liability. To the maximum extent permitted by law, infoz.com, Netlink BVI Ltd, and the authors disclaim liability for any direct, indirect, consequential, or incidental loss arising from use of this calculator or reliance on its output. You assume all risk of your reliance on the result.

Assumptions baked in:

Constant real return rate over the entire horizon.
Employer match is pre-tax and goes to a traditional 401(k) on both paths.
Marginal tax rates reflect federal-only; state tax differences not modeled.
No catch-up contributions or other age-specific limits applied.
Same dollar amount of pre-tax salary is committed to saving on both paths.

What this calculator does NOT cover:

Roth IRA income phase-out (high earners blocked from direct contributions).
Backdoor Roth, mega-backdoor Roth strategies.
401(k) contribution and IRA contribution IRS limits.
Required Minimum Distributions (RMDs) from traditional accounts.
Catch-up contributions for age 50+ / age 60-63.
Social Security taxation rules in retirement (provisional income).
Sequence-of-returns risk in withdrawal phase.
State income tax differences between accumulation and retirement states.
Roth conversion ladder for early retirement.
Estate planning considerations (Roth's lack of RMDs, basis step-up on traditional).

Talk to a professional. For decisions that involve real money — filing a return, structuring compensation, choosing an investment strategy — consult a qualified, licensed professional who can review your full circumstances. The cost of one consultation is almost always less than the cost of a wrong decision.

See the full site-wide legal disclaimer and terms for additional notices, including AI-assisted content disclosures and third-party data attribution.

401(k) vs Roth IRA Optimizer

Last reviewed Apr 27, 2026 · SN

Frequently asked questions

Why does the optimizer focus on marginal tax rates?

Because pre-tax-vs-post-tax retirement contribution math collapses to: which marginal rate is higher — now or in retirement? If now > retirement, traditional wins. If retirement > now, Roth wins. If equal, they're a tie (assuming the same return path and contribution limits). Real life adds complications (RMDs, state taxes, Social Security taxation), but the marginal rate is the dominant lever.

What about the employer match?

Employer 401(k) matches are always pre-tax — they go into a traditional 401(k) regardless of whether you contribute to a Roth. The calculator includes the match on both sides, which is why declining the match is never sensible. Always capture the full match before deciding pre-tax vs. Roth for the rest.

Are contribution limits checked?

No. The calculator runs whatever annual contribution you enter. Real IRS limits for 2026 are roughly $24,500 employee 401(k) and $7,500 IRA (placeholders pending final IRS notice). Roth IRA also has an income phase-out — high earners are blocked from direct Roth contributions and may need a backdoor Roth instead. The optimizer ignores these.

What about RMDs?

Required Minimum Distributions kick in at age 73 (or 75, depending on birth year per the SECURE 2.0 Act) and force traditional 401(k) / IRA balances to be drawn down on a schedule, possibly at higher tax rates. Roth accounts have no RMDs. The calculator does not model this; in practice it favors Roth somewhat at very high balances.

Is this advice?

No. For advice on your specific situation, talk to a fiduciary fee-only financial planner — and consider that pre-tax vs Roth is one of the highest-leverage decisions in retirement planning, so it pays to get it right.

401(k) vs Roth IRA Optimizer

Traditional 401(k)

Roth IRA

How this calculator works

Worked example: Age 35 → 65, $23,500 pre-tax, current rate 32%, retirement rate 12%, 6% real, 50% match

Sources & methodology

Frequently asked questions

Related

Important disclaimers

401(k) vs Roth IRA Optimizer

Traditional 401(k)

Roth IRA

How this calculator works

Worked example: Age 35 → 65, $23,500 pre-tax, current rate 32%, retirement rate 12%, 6% real, 50% match

Sources & methodology

Frequently asked questions

Related

Important disclaimers