Roth TSP vs. Traditional TSP: The Federal Employee's Decision Guide

The choice isn't about which is "better" — it's about when you pay taxes. Roth: pay now, withdraw tax-free. Traditional: defer now, pay at withdrawal. The math favors Roth when your rate rises; Traditional when it falls. Here's how to apply that to your actual situation.

How the tax math works

Traditional TSP: contributions reduce this year's taxable income dollar-for-dollar. You save your current marginal rate today. At withdrawal, the entire balance — contributions plus decades of growth — is taxed as ordinary income.

Roth TSP: contributions are made with after-tax dollars (no deduction today). But qualified distributions — after age 59½ and the 5-year holding period — are completely tax-free. Zero federal tax on decades of compounding.

The crossover: if your marginal rate in retirement exactly equals your marginal rate today, both approaches produce identical after-tax wealth. Traditional wins if your retirement rate is lower; Roth wins if it's higher.

2026 federal tax brackets in context

These are taxable income thresholds after the standard deduction ($16,100 single / $32,200 MFJ) and before any additional deductions.¹

Single filers:

Married filing jointly:

Note: traditional TSP contributions reduce your taxable income directly — every $1,000 contributed pre-tax saves you $220–$240 in federal taxes if you're in the 22–24% bracket. This lowers the effective bracket shown above.

What federal retirees actually earn — the retirement income stack

The bracket question isn't just about your working salary. It's about the income stack in retirement:

• FERS basic annuity arrives first. A GS-12–14 employee retiring after 28–30 years typically receives $35,000–$65,000/year — taxable as ordinary income federally (most states exempt it fully or partially).
• Social Security adds another $20,000–$40,000/year depending on earnings history and claiming age. Up to 85% of SS is included in taxable income if combined income exceeds $44,000 (MFJ) or $34,000 (single).²
• TSP withdrawals stack on top of those two. At modest withdrawal rates (3–4%), a $800K–$1.4M TSP balance adds another $24,000–$56,000/year.

The result: most FERS retirees with meaningful TSP balances land solidly in the 22% bracket in retirement, not 12%. The "I'll be in a lower bracket" assumption is often wrong — especially once Social Security taxation kicks in.

When Roth TSP makes the most sense

1. You're early in your career and in a low bracket now

If you're a GS-7 or GS-9 single filer with taxable income in the 12% bracket and you expect promotions into GS-12–15 over your career, Roth TSP locks in the low rate today. Even if you expect to be in 22% in retirement (roughly the same as your future working-years bracket), the 12% rate today is a genuine bargain — you're prepaying taxes at a rate that's almost certain to rise for you personally.

2. You already have a large traditional TSP balance

If you've accumulated $600K–$1.4M in traditional TSP (common for long-career GS-13–15 employees), your RMDs at age 73 will be substantial — potentially $40,000–$100,000/year on top of pension and SS. Adding Roth TSP contributions now builds a tax-free pool you can draw from in early retirement to control taxable income, stay below IRMAA Medicare surcharge thresholds, and reduce the eventual RMD burden.

3. You expect to be in a high income state in retirement

If your state taxes TSP distributions heavily (California, New York, New Jersey, Minnesota all tax federal retirement income at ordinary rates), Roth TSP distributions are tax-free at the state level too. The combined federal + state benefit of Roth is more compelling in high-tax states.

4. You want to maximize inheritance to heirs

Roth TSP can be rolled to a Roth IRA at separation, which passes tax-free to beneficiaries. Under current inherited IRA rules (post-SECURE Act 1.0 and T.D. 10001), most non-spouse beneficiaries must empty the account within 10 years — but Roth growth during that 10-year window is still tax-free. For high-balance accounts intended to pass wealth, Roth is meaningfully more valuable.

When Traditional TSP makes the most sense

1. You're in the 24%+ bracket now and expect a clear drop in retirement

A GS-15 single filer in a high-cost-of-living locality, currently at the top of the 22% bracket or into 24%, who plans to retire to a low-cost state with a modest FERS annuity and deliberately delay Social Security may genuinely face a 12% marginal rate on TSP withdrawals in their early retirement years. Traditional TSP saves 22–24% now and pays 12% later. That's a clear win.

2. You need the current-year deduction for cash flow

At the 24% bracket, $24,500 in pre-tax traditional TSP contributions saves $5,880 in federal taxes this year — money you keep and can invest elsewhere. If that cash flow matters (student loans, mortgage, kids' tuition, building taxable account), the deduction today has real value. Roth gives you none of that.

3. You're near retirement and won't have time for Roth compounding to pay off

The math advantage of Roth depends partly on how long the money compounds tax-free. If you're 58 and planning to retire at 62, you have a shorter runway for tax-free growth. Traditional TSP may produce more after-tax wealth in a shorter horizon if it means you keep more money working now.

The split strategy: why most advisors suggest both

Most fee-only advisors who work with federal employees recommend a split allocation — some Roth, some Traditional — rather than an all-or-nothing approach. The combined contribution limit is $24,500 regardless of how you allocate; you just tell your payroll system what percentage goes to each.

Reasons the split makes sense:

• Tax-rate uncertainty. Nobody knows what Congress does to rates over a 30-year career. Owning both pre-tax and post-tax TSP balances gives you options regardless of which way rates move.
• Withdrawal flexibility. In years when you have large one-time expenses (home repairs, healthcare, helping a child), you can draw from traditional or Roth depending on which creates less tax drag that year.
• IRMAA management. Medicare Part B and D surcharges kick in at income thresholds (around $106,000 for single filers in 2026). Roth TSP withdrawals don't count as income — so you can supplement spending from Roth without triggering IRMAA surcharges that can run $1,000–$5,000/year.
• Social Security optimization. The 85% SS inclusion threshold means TSP income can push more of your SS into taxable territory. Roth TSP distributions avoid this. Using Roth in years when you're delaying SS (and SS isn't counted yet) preserves more traditional TSP for later years when your bracket may actually be lower.

2026 rule change: mandatory Roth catch-up for high earners

Starting January 1, 2026, SECURE 2.0 Act § 603 requires that if your prior-year wages from TSP-eligible federal positions exceeded $150,000 (indexed annually), all of your catch-up contributions must go to Roth TSP — you cannot direct them to traditional.³

The 2026 catch-up limits:

• Ages 50–59 and 64+: $8,000 catch-up → total $32,500 if mandatory Roth catch-up applies, it all goes to Roth TSP
• Ages 60–63 (super catch-up): $11,250 → total $35,750, also mandatory Roth if above income threshold⁴

If this applies to you, your TSP administrator will automatically redirect contributions to Roth once you hit the $24,500 base limit. You don't need to take action — but you should know it's happening so you can adjust your overall tax planning accordingly.

For high earners who preferred traditional catch-up contributions for the deduction, this change forces Roth exposure they may not have chosen. On the other hand, it automatically builds Roth diversification without requiring the decision.

SECURE 2.0 § 325: Roth TSP no longer has lifetime RMDs (effective 2024)

Before 2024, Roth TSP was subject to required minimum distributions beginning at age 73 — identical to traditional TSP. This was a significant disadvantage vs. Roth IRAs, which have no lifetime RMDs for the original owner.

SECURE 2.0 § 325 changed this: starting in 2024, Roth TSP balances are excluded from the RMD calculation entirely. Only your traditional TSP balance drives the RMD amount.⁵

What this means in practice:

• You no longer need to roll Roth TSP to a Roth IRA at separation just to avoid RMDs. You can leave it in TSP.
• A federal employee with $800K traditional / $200K Roth TSP calculates RMDs only on the $800K, not the full $1M.
• Roth TSP continues compounding tax-free without forced distributions.

Roth TSP → Roth IRA: when rolling makes sense even without the RMD reason

Even though Roth TSP now avoids lifetime RMDs, you may still want to roll it to a Roth IRA at separation:

• Investment options: Roth IRA holds any ETF, individual stock, or bond fund — not just TSP's 5 core funds.
• Beneficiary flexibility: Roth IRA allows more sophisticated beneficiary designations (trusts, per-stirpes elections, multiple beneficiaries).
• No 5-year rule restart: when you roll Roth TSP to Roth IRA, the IRA inherits the TSP's 5-year clock — it doesn't reset to zero.
• IRMAA strategy: some advanced Roth conversion ladder strategies require an IRA specifically; TSP can't be a Roth conversion target from outside.

The case to leave Roth TSP in TSP: if you value simplicity, have a large G Fund allocation you want to keep (G Fund is unavailable outside TSP), or plan to keep working for another agency — stay in TSP and simplify later.

What you cannot do: no in-plan Roth conversions

Unlike some private-sector 401(k) plans, TSP does not allow in-plan Roth conversions. You cannot take a traditional TSP balance and convert it to Roth TSP within the plan.

To do a Roth conversion from TSP, you must:

1. Separate from federal service (or reach age 59½ for an in-service withdrawal).
2. Roll the traditional TSP balance to a traditional IRA.
3. Convert the traditional IRA to Roth IRA — paying ordinary income tax in the conversion year.

This matters for the "FERS retirement window" strategy: many FERS retirees have 5–13 years between retirement (as early as age 57 at MRA+30) and when RMDs start (age 73). During that window, with income lower than working years, Roth conversions can make sense. But to use this tool, you need money in an IRA — not in TSP. If you're planning a Roth conversion ladder, factor in rolling at least part of traditional TSP to a traditional IRA at separation.

Decision summary

Sources

1. IRS Rev. Proc. 2025-32 — 2026 tax brackets, standard deduction, and inflation adjustments. Standard deduction: $16,100 single / $32,200 MFJ. 22% bracket: $50,401–$105,700 (single), $100,801–$211,400 (MFJ).
2. SSA.gov — Benefits Planner: Income Taxes and Your Social Security Benefits. Up to 85% of SS taxable above $34,000 (single) / $44,000 (MFJ) combined income threshold.
3. TSP.gov — SECURE 2.0 and the TSP. § 603 mandatory Roth catch-up effective January 1, 2026 for participants with prior-year wages above $150,000 threshold.
4. TSP.gov — Contribution Limits. 2026: $24,500 base; $8,000 catch-up (ages 50–59 and 64+); $11,250 super catch-up (ages 60–63 per SECURE 2.0 § 109).
5. TSP.gov — SECURE 2.0 § 325. Roth TSP balances excluded from required minimum distribution calculation effective 2024.

Tax brackets and TSP contribution limits verified against IRS Rev. Proc. 2025-32 and TSP.gov as of April 2026. Consult a tax professional before making TSP contribution elections — individual circumstances vary significantly.