Model after-tax retirement wealth between pre-tax and Roth accounts. Identify your exact break-even retirement tax rate and evaluate how tax changes impact your future spendable income.
Roth receives after-tax equivalent so your take-home pay is identical.
Federal + State marginal
Blended rate on withdrawals
Under current IRS tax rules, employer match dollars grow pre-tax and are taxed as ordinary income upon distribution.
Marginal vs Effective Arbitrage: You save taxes at your marginal rate today (highest bracket), while retirement withdrawals fill brackets from 0% (standard deduction) upwards, resulting in a lower effective rate unless other pensions exist.
Estimated After-Tax Retirement Wealth Winner
Because your effective retirement tax rate (15%) is lower than today's marginal bracket (24%), traditional pre-tax contributions give you a significant tax arbitrage advantage.
Deduct at 24% today • Taxed at 15% upon withdrawal
Pay 24% today • 100% Tax-Free withdrawals in retirement
How unexpected legislative tax hikes or lower retirement brackets shift the winning account
| Retirement Tax Scenario | Future Rate | Traditional After-Tax | Roth After-Tax | Advantage |
|---|---|---|---|---|
| 10% Lower in Retirement | 14.0% | $754,717 | $687,211 | Trad +$67,506 |
| 5% Lower in Retirement | 19.0% | $710,838 | $677,085 | Trad +$33,753 |
| Parity (Break-Even) | 24.0% | $666,959 | $666,959 | Break-Even |
| 5% Higher in Retirement | 29.0% | $623,080 | $656,833 | Roth +$33,753 |
| 10% Higher in Retirement | 34.0% | $579,201 | $646,707 | Roth +$67,506 |
The Tax Diversification "Three Buckets" Rule: Financial planners rarely recommend putting 100% of your assets into a single wrapper. Holding money in pre-tax (Traditional), tax-free (Roth), and taxable brokerage accounts lets you manage your annual taxable income in retirement to avoid higher Medicare IRMAA surcharges and Social Security taxation.
SECURE 2.0 & RMD Flexibility: Roth accounts are exempt from Required Minimum Distributions (RMDs) during your lifetime. If you plan to leave wealth to heirs or delay withdrawals beyond age 73–75, Roth dollars offer vastly superior generational wealth protection.
State Relocation Strategy: If you currently work in a high-tax state (e.g., California, New York, New Jersey) and intend to retire in a state with zero income tax (e.g., Florida, Texas, Nevada, Washington), your effective retirement tax rate drops sharply, strongly favoring Traditional 401(k) contributions today.
Both accounts shelter growth from annual taxes; the difference is timing. Traditional contributions skip income tax now but are taxed as ordinary income at withdrawal. Roth contributions use after-tax dollars and come out completely tax-free after age 59½. This calculator holds total purchasing power constant, applies each wrapper's tax treatment, and declares a winner in after-tax dollars. Brush up on brackets in our federal tax guide.
Employees splitting payroll deferrals between Roth and pre-tax 401(k), early-career savers in low brackets, peak earners eyeing deductions, and anyone expecting bracket changes from retirement timing, state moves, or RMD-driven income. Pairs naturally with our tax withholding calculator.
Example Input
Contribution capacity: $8,000/yr pre-tax equivalent. Current bracket: 22%. Expected retirement bracket: 12%. Growth: 7% for 30 years.
Sample Output
Roth wins by a wide margin: paying 22% now instead of 12% later leaves roughly 27% more after-tax wealth despite identical gross growth.
Example Input
Same contributions but current bracket 35%, retirement bracket 22%.
Sample Output
Traditional wins: deducting dollars at 35% and withdrawing at 22% preserves roughly 20% more spendable retirement income than Roth contributions would.
Each open enrollment, after raises that shift your marginal bracket, when planning a low-income gap year ideal for Roth conversions, and when estimating whether today's national-debt-driven future tax assumptions justify hedging with Roth dollars.
Fix a pre-tax contribution budget, then apply your current marginal rate to compute the smaller Roth contribution with equal upfront cost. Grow both at the same return for the same years. Apply your assumed retirement rate to traditional withdrawals only. The larger after-tax figure wins; the delta quantifies the decision's stakes.
The single biggest error is comparing nominal balances instead of after-tax values. Others: using effective rather than marginal rates for the deduction side, ignoring that diversifying across both types hedges legislative risk, forgetting employer matches land pre-tax regardless of your election, and assuming your retirement bracket stays static through RMDs and Social Security.
If your marginal tax rate today is lower than your expected rate in retirement, choose Roth; if higher, choose traditional; if similar, split the difference. Early-career and entry-level savers usually favor Roth, while peak earners favor pre-tax deductions.
Yes, most plans allow any split of one combined elective deferral limit. Many savers hedge uncertainty with something like 70/30 or 50/50 rather than betting entirely on one tax outcome.
Yes, Required Minimum Distributions begin in your 70s (age set by current law, 73-75 range depending on birth year) and push taxable income up, potentially raising Medicare premiums. Roth 401(k) balances gained RMD exemption under SECURE 2.0 via in-plan rollover rules; verify your plan's provisions.
The comparison is driven mainly by the tax rate when contributing versus the tax rate when withdrawing, plus contribution limits, growth period, employer match, and how the contribution budget is framed. Test both current and future tax-rate assumptions.
Deterministic math runs instantly in your browser on any modern device, with no login and no data retention. Move the bracket sliders and watch the crossover point appear, giving you conviction rather than generic internet advice.
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