TSP Traditional vs Roth

I The core question in one sentence

The Traditional vs Roth TSP decision reduces to a single question: will your marginal tax rate in retirement be higher or lower than your marginal tax rate today? If lower, contribute to Traditional. If higher, contribute to Roth. If roughly equal, either works and splitting between them provides useful tax diversification.

Everything else — asset location theory, Roth conversion ladders, backdoor Roth strategies, tax diversification arguments — is secondary to this core question. Federal employees who get the primary decision right will do fine even with imperfect optimization of the surrounding details. Federal employees who get the primary decision wrong will lose meaningful lifetime wealth regardless of how carefully they optimize the surrounding details.

The complexity comes from estimating your retirement marginal rate. That estimate requires modeling your expected FERS pension, Social Security benefits, TSP withdrawals, and any other income (rental property, part-time work, spouse income), then applying the tax brackets you expect in your retirement years. For most federal employees, retirement income is substantially higher than they anticipate — the combination of FERS pension + Social Security + TSP RMDs frequently produces 60-90% of pre-retirement income. This inflates retirement marginal rates and often makes Roth more attractive than intuition suggests.

II How Traditional and Roth actually differ

Both Traditional and Roth TSP are payroll-deducted contributions to your TSP account. The differences are entirely in the tax treatment:

Traditional TSP contributions are made with pre-tax dollars. Your contribution reduces your current federal taxable income dollar-for-dollar. Investment growth is tax-deferred — you pay no tax on interest, dividends, or capital gains inside the account. When you withdraw in retirement, both your contributions and their growth are taxed as ordinary income at whatever rate applies in the year of withdrawal.

Roth TSP contributions are made with after-tax dollars. Your contribution does NOT reduce your current federal taxable income. Investment growth is tax-free. Qualified withdrawals in retirement (age 59½+ and account held 5+ years) are entirely tax-free — no federal income tax on either contributions or growth.

Both options share the same $24,500 combined elective deferral limit for 2026, the same agency matching mechanics (with match always deposited to Traditional), the same investment fund choices, and the same withdrawal rules with two exceptions: Roth TSP qualified withdrawals are tax-free, and Roth TSP is subject to RMDs during your lifetime after age 73 or 75 (depending on birth year) — a disadvantage compared to Roth IRA which has no lifetime RMD requirement. Federal employees who want to preserve Roth balances for heirs often roll Roth TSP to a Roth IRA after separation.

III The 2026 federal tax brackets in context

The 2026 federal marginal tax brackets, as published under IRS Revenue Procedure 2025-32 (October 2025), reflect the OBBBA (One Big Beautiful Bill Act) permanent extension of the TCJA rate structure plus inflation adjustments:

The critical numbers for TSP decisions:

• The 12%-to-22% cliff — a $9.90 tax jump per $100 of additional income — is the most consequential threshold. Federal employees whose taxable income sits just above this line have very different Roth math than those just below.
• The 24%-to-32% cliff is the second consequential threshold. It affects most GS-14 and GS-15 employees in high-locality areas.
• Federal employees paying Additional Medicare Tax (0.9%) at higher incomes and Net Investment Income Tax (3.8%) on unearned income effectively face marginal rates 4.7 percentage points higher than the stated bracket. For a GS-15 in the 32% bracket with investment income, the true marginal rate on the next dollar of Traditional TSP contribution deferral savings is 36.7% federal alone.

For a federal employee to calculate their exact marginal bracket, subtract standard deduction ($16,100 single or $32,200 MFJ) plus any pre-tax deductions (existing Traditional TSP contributions, FSAFEDS, health insurance premiums) from gross income to arrive at taxable income, then locate that taxable income in the appropriate bracket table above.

For the pay data that feeds into these calculations, see the 2026 GS Pay Calculator and Career & Pay Topic 01 on the GS Scale.

IV The breakeven analysis

The mathematical reason the Traditional vs Roth decision hinges on tax rates is straightforward. Compare two federal employees each contributing $10,000 of pre-tax income to TSP:

Employee A — Traditional TSP: Contributes the full $10,000 (pre-tax). No current tax owed. Amount grows over 25 years at 6% annually to $42,919. In retirement at a 22% marginal rate, pays $9,442 in tax on withdrawal, leaving $33,477 after-tax.

Employee B — Roth TSP: Pays 22% tax on the $10,000 first, so has $7,800 to contribute (after $2,200 in tax). $7,800 grows over 25 years at 6% to $33,477. Withdrawal in retirement is tax-free — full $33,477 in hand.

The after-tax amounts are identical: $33,477. When your current marginal rate equals your retirement marginal rate, Traditional and Roth produce mathematically identical after-tax outcomes.

The math shifts when the rates differ:

• Current 12% → Retirement 22%: Traditional produces $33,477 after-tax; Roth produces $37,769 after-tax. Roth wins by $4,292 (12.8%).
• Current 22% → Retirement 12%: Traditional produces $37,769 after-tax; Roth produces $33,477 after-tax. Traditional wins by $4,292 (12.8%).
• Current 24% → Retirement 22%: Traditional produces $33,477; Roth produces $32,618. Traditional wins by $859 (2.6%).
• Current 32% → Retirement 24%: Traditional produces $32,618; Roth produces $29,185. Traditional wins by $3,433 (11.8%).

The pattern: the larger the gap between current and retirement marginal rates, the more the "better" option outperforms. For federal employees in the 12%-to-22% transition zone (GS-9 to GS-12 range), the future tax picture is the dominant variable.

Why federal employees underestimate retirement marginal rates

The most common mistake in the Traditional vs Roth decision is assuming retirement income will be substantially lower than working income. Federal employees have three retirement income sources that most private-sector employees don't:

• FERS pension at typically 1% × years × high-3 (or 1.1% if retiring at 62+ with 20+ years). For a 30-year GS-13 retiring at 60, this is approximately $41,400 annually — fully taxable.
• Social Security at approximately 30-40% of final salary for high-earners with full working history. For the same GS-13, approximately $30,000-40,000 annually — up to 85% taxable at federal level.
• TSP RMDs starting at age 73 or 75 depending on birth year. For a TSP balance of $800,000 at age 75, the RMD is approximately $32,500 — fully taxable if Traditional.

Adding these three streams for the 30-year GS-13 retiree produces approximately $114,000 in retirement income — placing them in the 22% marginal bracket, only one bracket below their likely working marginal bracket. Federal employees whose retirement modeling doesn't include Social Security or RMDs will systematically underestimate retirement tax rates and over-select Traditional TSP.

For the full retirement income modeling framework, see Topic 11 on FERS Accrual & High-3 Mechanics and the TSP Projector tool.

V The agency match — always Traditional

An important structural point that changes the composition of every federal employee's TSP: the agency automatic 1% contribution and the agency matching contribution (up to 4%) are ALWAYS deposited to Traditional TSP, regardless of whether your own contributions are Traditional or Roth. This is a statutory requirement, not a TSP policy choice — 5 U.S.C. 8432 specifies that agency contributions are traditional pre-tax contributions.

The practical implication: even federal employees who contribute 100% to Roth TSP end up with mixed Traditional and Roth balances at retirement. The Traditional portion — funded entirely by agency money — grows tax-deferred and is taxed as ordinary income at withdrawal. For a career federal employee contributing 5% Roth for 30 years and earning the full 5% agency contribution, the Traditional portion of the ending balance is roughly equal in size to the Roth portion.

This has three consequences:

• You cannot "opt out" of having any Traditional TSP balance while receiving the agency match. If you want zero Traditional balance, you'd have to forgo agency contributions entirely, which is never worth doing.
• Federal employees planning for tax-free retirement income need to account for the mandatory Traditional portion in RMD planning. Roth withdrawals are tax-free; Traditional withdrawals are taxable.
• The Traditional agency-contribution portion gives every federal employee some baseline tax diversification even without an explicit split-contribution strategy.

For detailed agency match mechanics see Topic 12 on TSP Contribution Strategy.

VI Traditional vs Roth Recommender

Enter your details below. The tool applies the 2026 tax brackets to your specific situation and returns a Traditional or Roth recommendation with the estimated after-tax wealth difference over a typical 25-year contribution horizon.

VII Recommendations by GS grade and career stage

The following recommendations assume the federal employee is in the Rest of U.S. or a moderate locality area, working toward a full career (25+ years FERS service), and expects to retire between ages 57-65. Adjustments for special situations follow in section XI.

GS-5 to GS-9 (early career, taxable income roughly $30K-$70K)

Recommendation: 100% Roth TSP. These employees are in the 12% or low 22% bracket now. Their retirement marginal rate will almost certainly be at least 22% and possibly higher after career growth, pension, and Social Security. Roth captures cheap tax now, produces tax-free retirement income, and hedges against the possibility that federal tax rates rise before their retirement (a real risk given projected long-term federal deficits and the OBBBA sunset provisions on certain individual tax reforms in 2028+).

GS-10 to GS-12 (mid-early career, taxable income roughly $70K-$110K)

Recommendation: 60-100% Roth TSP. These employees are typically in the 22% bracket. Their retirement marginal rate is likely to be similar (22%) or one bracket higher (24%). Roth is generally favored for tax diversification, retirement flexibility (no RMDs on Roth IRA after rollover), and hedging against future rate increases.

GS-13 (mid-career, taxable income roughly $110K-$160K)

Recommendation: 40-60% Roth, 40-60% Traditional (split). The transition zone. GS-13s in low-locality areas may sit in the 24% bracket; those in high-locality areas may cross into 32%. Retirement marginal rate is uncertain — likely 22-24%, but depends heavily on TSP balance size at RMD age. Splitting contributions between Traditional and Roth provides tax diversification and hedges the uncertainty.

GS-14 (senior professional, taxable income roughly $160K-$220K)

Recommendation: 70-100% Traditional TSP. These employees are firmly in the 24% or 32% bracket. Retirement marginal rate is likely 22-24% — a full bracket lower than working. Traditional captures the current high-bracket deferral and pays tax at the lower retirement rate. The mandatory Roth catch-up under SECURE 2.0 §603 provides some Roth exposure for high earners without requiring an explicit split election.

GS-15 and SES (executive, taxable income $220K+)

Recommendation: 100% Traditional TSP for elective deferral portion; mandatory Roth on catch-up under SECURE 2.0. These employees are in the 32%, 35%, or 37% bracket. Their retirement marginal rate is very likely 24-32%. Traditional captures the maximum current deferral. The mandatory Roth catch-up provides tax-free retirement growth. Post-retirement, strategic Roth conversions during low-income years can convert additional Traditional to Roth at controlled tax rates.

Special early-career situation: student loan repayment

Federal employees participating in Public Service Loan Forgiveness (PSLF) benefit from Traditional TSP because it reduces adjusted gross income (AGI), which in turn reduces income-driven repayment (IDR) monthly payments. Roth TSP does not reduce AGI. For PSLF-eligible employees still in the qualifying payment period, Traditional TSP produces both retirement wealth and reduced monthly loan payments — a double benefit that shifts the calculus toward Traditional even for lower-grade employees. See Professional Development Topic on PSLF.

VIII State tax and geographic arbitrage

State income tax has a substantial impact on the Traditional vs Roth decision that federal advice frequently overlooks. If you contribute to Traditional TSP while working in a high-state-tax jurisdiction (California 9.3%+, New York 6.85%+, New Jersey 5.5%+, Oregon 8.75%, Massachusetts 5%) and then retire in a no-income-tax state (Florida, Texas, Nevada, Washington, Tennessee, South Dakota, Wyoming, Alaska), you capture a permanent state-tax arbitrage worth 5-10% of every dollar contributed.

Consider a GS-14 in Washington DC (0% DC state income tax on nonresidents, but Maryland or Virginia residency taxes at 5.75% and 5.75% respectively) contributing to Traditional TSP for 25 years then retiring to Florida. Traditional captures the federal deferral (savings at 24-32% federal marginal rate) plus permanent avoidance of state tax on both the contribution and its growth. The Roth alternative would have paid state tax now with no state tax on retirement withdrawals — but the retirement state has no income tax anyway, so Roth's state-tax benefit is zero.

Conversely, federal employees who plan to remain in a high-state-tax state throughout retirement — or move to one — should lean more toward Roth to lock in the current state tax cost and produce tax-free retirement income in the same jurisdiction.

Federal employees planning geographic retirement should factor state tax explicitly into their Traditional vs Roth decision. The duty-station and locality mechanics that shape the working-years half of that plan are covered in Career & Pay Topic 22 on changing your official duty station, and the High-3 consequences of a late-career move are in Topic 35 on High-3 optimization.

IX SECURE 2.0 §603 mandatory Roth catch-up

Effective January 1, 2026, Section 603 of the SECURE 2.0 Act imposes a new requirement on high-earning federal employees making catch-up contributions. Federal employees whose 2025 FICA wages (Box 5 of the 2025 W-2) exceeded $150,000 must direct all catch-up contributions to Roth TSP. The traditional pre-tax catch-up option is eliminated for these high earners.

The mechanics:

• Threshold basis: Prior-year FICA wages (Medicare wages, Box 5 of W-2), not gross income. FICA wages include most pre-tax deductions added back.
• Threshold amount: $150,000 in 2025 wages triggers the rule for 2026 catch-up contributions.
• Effective date: January 1, 2026 (delayed twice from original 2024 effective date).
• Applies to: Both the $8,000 standard catch-up (age 50+) and the $11,250 super catch-up (ages 60-63).
• Does NOT apply to: The underlying $24,500 elective deferral portion. This can still be allocated freely between Traditional and Roth.
• Automatic: The TSP spillover mechanism automatically directs post-$24,500 contributions to Roth if you meet the high-earner criteria. No separate election required.

The rule affects a substantial fraction of GS-14 and GS-15 employees in high-locality areas. It also creates a new after-tax cash flow requirement: at a 24% marginal rate, an $8,000 Roth catch-up requires approximately $10,530 of pre-tax gross income to fund. Federal employees who were budgeting for pre-tax catch-up should adjust household budgets accordingly.

Strategically, the mandatory Roth catch-up is not a bad outcome for most high-earning federal employees — Roth provides valuable tax diversification and hedges against the possibility of higher federal tax rates in retirement. But the cash flow requirement is real and needs to be planned for.

X Splitting contributions and tax diversification

TSP allows any percentage split between Traditional and Roth. The election is made through your agency payroll system alongside your total contribution amount — you specify a total percentage or dollar amount, then indicate what portion goes to Traditional vs Roth. Changes can be made as often as payroll systems allow.

Splitting is often the right answer when:

• You are in the GS-12 to GS-13 transition zone where the correct answer is genuinely uncertain
• You value tax diversification in retirement — having both taxable and tax-free withdrawal sources gives flexibility to manage withdrawals across tax brackets
• You expect substantial income uncertainty in retirement (self-employment, rental income, spouse income variability)
• You anticipate needing to manage Social Security taxation thresholds — Roth withdrawals don't count toward the "combined income" formula that determines Social Security taxability
• You want to hedge against federal tax rate uncertainty

Common split strategies:

• 50/50 straight split. Simple, provides balanced tax diversification, appropriate for GS-12/13 employees uncertain about retirement bracket.
• Age-based transition. 100% Roth in early career, shift to 100% Traditional as you approach senior grades. Captures Roth benefit at low current rates and Traditional benefit at high current rates.
• Grade-based ratio. Roth percentage roughly matches (100 - GS grade × 5). GS-11 → 45% Roth. GS-13 → 35% Roth. GS-15 → 25% Roth. Rough heuristic but produces reasonable outcomes for most careers.

XI Special situations that change the math

Uniformed services in combat zones

Combat zone contributions to Traditional TSP are made with tax-excluded income. The contributions and their growth are still tax-deferred, but the retirement withdrawal is fully taxable at ordinary rates — creating a worst-case scenario of tax-free income becoming taxable at retirement. Combat zone contributions should generally go to Roth TSP where they remain fully tax-free at both ends.

Planned early retirement (before age 59½)

Federal employees planning to retire under FERS MRA + 10 or FERS deferred retirement provisions may need bridge income before age 59½ when TSP withdrawals become fully accessible. Traditional TSP withdrawals before 59½ typically incur the 10% early withdrawal penalty in addition to ordinary income tax. Roth TSP contributions (not earnings) can be withdrawn without penalty after 5 years — providing more flexibility for early-retirement bridge income. Federal employees planning early retirement benefit from Roth's flexibility even when the tax-rate analysis alone might favor Traditional.

Substantial expected inheritance

Federal employees expecting significant inheritance in retirement should consider that the inherited assets will likely be invested and generate ongoing income — pushing retirement marginal rates higher. Under this scenario, Roth TSP produces greater lifetime after-tax wealth because the tax-free retirement income doesn't compound with the inherited-asset income to push into higher brackets.

Federal employees who plan to work past age 65

Federal employees continuing to work past age 65 face the "Social Security earnings test" (removed at Full Retirement Age but still a consideration for benefit optimization) and potential Medicare IRMAA premiums driven by MAGI. Roth TSP withdrawals don't add to MAGI; Traditional TSP withdrawals do. For employees planning phased retirement or bridge work, Roth provides better protection against IRMAA cliff pricing.

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