Roth vs Traditional TSP in 2026: The Decision After Two Changes

1. What changed in 2026 — and why the old advice broke

Two changes hit federal employees on essentially the same calendar:

• January 1, 2026: SECURE 2.0 §603 took effect. Federal employees age 50 or older who earned more than $150,000 in 2025 FICA wages are now required to make all catch-up contributions to Roth TSP. Traditional catch-ups are no longer an option for them.
• January 28, 2026: The TSP launched in-plan Roth conversions. Participants can now convert traditional TSP money to Roth TSP without rolling money out of the plan to an IRA. The feature is irrevocable, taxable in the year converted, and minimum $500 per conversion.

Both changes make the Roth versus Traditional TSP decision more practical to act on. Neither change makes Roth automatically better.

There’s a third change worth flagging up front, because it invalidates one of the most common Roth talking points: the One Big Beautiful Bill Act, signed July 4, 2025, made the 2017 TCJA tax brackets permanent. For years, financial advisors had been telling federal employees, "Convert to Roth before 2026, because tax rates are scheduled to rise when TCJA expires." That expiration didn’t happen. The brackets stayed at 10%, 12%, 22%, 24%, 32%, 35%, and 37%. The "tax brackets will be higher in retirement than today" argument now needs to be made on the basis of your future tax situation, not the statute book.

2. The core difference, restated cleanly

For federal employees still building toward retirement, the fundamental tradeoff hasn’t changed:

Two TSP-specific quirks deserve flagging immediately:

The agency match is always Traditional. Whatever you elect for your own contributions, the 1% automatic agency contribution plus the up-to-4% match always lands in your Traditional balance. There’s no version of TSP where your match goes Roth. (After the January 2026 in-plan conversion launch, you can now convert that traditional match balance to Roth — but you pay tax on the conversion.)

Roth TSP and Roth IRA are different. Until 2024, Roth TSP balances were subject to Required Minimum Distributions. That rule changed under SECURE 2.0 — Roth TSP balances no longer require RMDs at 73. This was a major win for retirement-strategy purposes and it brought TSP into alignment with Roth IRA rules.

For more on how TSP differs from outside retirement accounts in general, see Half of Americans have no retirement account. Federal employees with TSP are already ahead.

3. The mandatory Roth catch-up rule

Here’s the rule, distilled:

If you are age 50 or older in 2026 AND earned more than $150,000 in 2025 FICA wages from your federal employer, then any catch-up contributions in 2026 must go to Roth TSP. You no longer have the option of directing catch-up contributions to Traditional.

A few clarifications because this rule confuses everyone:

• The threshold is on prior-year wages, not current. For 2026 contributions, the IRS looks at your 2025 W-2 Box 5 (Medicare wages). For 2027 contributions, it will look at your 2026 wages.
• The statute says $145,000 indexed for inflation. The IRS adjusted it to $150,000 for 2026. It will likely rise again for 2027.
• Only catch-up contributions are affected. Your regular $24,500 contribution can still be Traditional, Roth, or split.
• Affected employees in 2026: Anyone over age 50 making more than about $150K. For federal employees, that’s the bulk of GS-13 and above in higher localities, most GS-14 and GS-15 employees regardless of locality, and a substantial portion of GS-12 employees in the DC, San Francisco, and New York localities.

What it costs you in current-year tax. Roth catch-up contributions are made with after-tax dollars, meaning your taxable income is higher than it would have been under the old Traditional catch-up. A GS-14 in the 24% bracket who maxes the standard $8,000 catch-up loses $1,920 in current-year tax savings they previously had access to. For someone hitting the 32% bracket on that marginal dollar, it’s $2,560.

That money isn’t gone — it’s now sitting in Roth, where it will grow tax-free and come out tax-free. But it changes your immediate cash flow.

What about ages 60-63 super catch-up? Same rule. The SECURE 2.0 enhanced catch-up (which raises the catch-up limit to $11,250 for those four ages) is also Roth-only for high earners. A 62-year-old GS-15 contributing the full $11,250 super catch-up will see those entire contributions land in Roth.

For a deeper look at how the catch-up windows compound over time, see The TSP balance you should have at every age.

4. The new Roth in-plan conversion option

The Roth in-plan conversion was the more anticipated of the two 2026 changes. For years, federal employees who wanted to do Roth conversions had to either: (a) move money out of TSP to a Traditional IRA first, then convert to a Roth IRA — a multi-step process — or (b) wait until separation and roll the whole balance out. The new in-plan feature eliminates both steps.

Here’s how it works mechanically:

The "5-year clock" you must understand. Each conversion starts its own five-year clock, beginning January 1 of the year of conversion. If you withdraw converted principal before five years AND you’re under 59½, you owe a 10% early-withdrawal penalty on that money. This is the same rule that has long applied to Roth IRA conversions.

The clock applies to converted principal, not earnings. Earnings on Roth TSP have their own separate five-year rule, starting January 1 of the year of your first Roth contribution or conversion.

The strategic case for converting. A Roth conversion makes sense when three conditions all line up:

1. You expect your tax rate in retirement to be higher than your current tax rate
2. You have cash outside TSP to pay the conversion tax
3. You don’t need the converted money for at least five years (or you’re already past 59½)

Federal employees with strong pensions are unusually positioned for this analysis. The FERS pension plus Social Security plus required Traditional TSP withdrawals can easily push a retiree into the 22% or 24% bracket even when they thought they’d be in 12%. RMDs at 73 are the moment many federal retirees discover this.

For a FERS retiree at 73, the combination of pension, Social Security, and required Traditional TSP distributions often stacks into the 24% bracket. The Roth conversion question is whether you’d rather pay 22% now in a controlled year — or 24% then in a forced one.

5. The five-year rule confusion

The single most confusing aspect of Roth TSP is that there are two different five-year rules, and most federal employees don’t know which one applies to them.

Rule #1: The earnings 5-year rule. Earnings on Roth TSP money are tax-free only if both: (a) you’re at least 59½ (or disabled or deceased), AND (b) at least five tax years have passed since January 1 of the year of your first Roth contribution or first Roth conversion.

So if you made your first Roth TSP contribution in 2024, your 5-year clock started January 1, 2024. Your earnings become fully tax-free starting in 2029, assuming you’re also 59½.

You only have to start the clock once. Subsequent contributions don’t restart it.

Rule #2: The conversion 5-year rule. Each individual Roth conversion starts its own five-year clock for the converted principal. If you withdraw converted money within five years AND you’re under 59½, you owe a 10% penalty on the converted amount.

After 59½, this rule effectively disappears for most retirees. If you’re already past 59½ when you convert, you can withdraw converted principal at any time without penalty.

6. The actual decision framework

Strip away the new-feature noise. The Roth vs Traditional decision still comes down to one fundamental question:

Will your marginal tax rate in retirement be higher, lower, or about the same as today?

If you can answer that honestly, the math follows.

Case 1: Future tax rate higher than today. Roth wins. Pay tax at today’s rate, lock in tax-free growth, withdraw tax-free later. Strong candidates: junior federal employees with long careers ahead, anyone expecting a sharp income increase, anyone with a large Traditional TSP balance heading toward RMD age.

Case 2: Future tax rate lower than today. Traditional wins. Deduct now at the higher rate, withdraw later at the lower rate. Strong candidates: late-career GS-14/15 employees in high-cost localities who plan to retire to lower-cost areas and lower-bracket retirements, employees in the 32%+ bracket who expect to retire into 22-24%.

Case 3: Roughly the same future tax rate. Roughly a wash mathematically, but Roth offers structural advantages: no RMDs, more flexibility on IRMAA management, better for heirs. In this case, default to Roth for the optionality.

The math is the same whether you’re contributing or converting. The difference between a contribution decision and a conversion decision is the timing of the tax bill.

The wildcard most federal employees miss: IRMAA. Medicare Part B and Part D premiums are income-tested. If your modified adjusted gross income in retirement exceeds certain thresholds, your Medicare premiums increase by hundreds of dollars per month. Traditional TSP withdrawals count toward MAGI. Roth withdrawals do not. For high-income retirees, the IRMAA differential alone can justify Roth heavily — even when the pure tax-bracket math is a coin flip.

A few patterns to notice. When current and retirement brackets are equal, Roth and Traditional produce mathematically identical after-tax outcomes — the choice is a wash on pure math, though Roth carries structural advantages (no RMDs, more IRMAA flexibility). When your current bracket is lower than your retirement bracket, Roth wins. When your current bracket is higher, Traditional wins. The biggest swings happen at extreme bracket differences: a 12% earner who retires into 22% gains roughly 13% in after-tax value from Roth, while a 32% earner who retires into 24% gains roughly 12% from Traditional.

7. Where federal employees most often get this wrong

After tracking federal-retirement forums and FRTIB participant data, the same patterns repeat:

"I’ll lower my taxes today, so Traditional is obviously better." This is the most common mistake. It ignores the back end. Lowering your taxes today only helps if your retirement tax rate is genuinely lower than today’s. For early-career employees with 30+ years of contributions ahead, that’s mathematically unlikely — your salary will rise, your TSP will grow, RMDs will kick in, and you’ll probably retire into a higher bracket than you started at.

"I’ll just split 50/50." Defensible but rarely optimal. Splitting 50/50 protects you against being wrong about future tax rates, but it also locks in tax diversification you may not actually need. A more deliberate approach: lean Roth in your low-earning years (junior career, low-locality assignments), lean Traditional in your high-earning years (late career, top step in high locality), and use the new in-plan conversions to rebalance later.

"I’m 5 years from retirement, I should convert everything to Roth now." This is rarely right. Converting a large Traditional balance in a single year stacks the entire conversion on top of your already-high working-year income. You’ll pay tax at your marginal rate — usually 24% or 32% — when you could have converted in lower-income retirement years at 12% or 22%. The best conversion years are typically the first 5-10 years of retirement, before RMDs and Social Security stack on top.

"The match is Traditional, so I should make my own contributions Roth for tax diversification." This logic is right in principle but often misapplied. The math depends entirely on your bracket. A GS-14 in the 24% bracket making Roth contributions is paying a 24% premium today for tax-free withdrawals decades away. That can pay off, but it’s not automatic.

"I’ll convert now before tax rates rise." Defunct as of July 2025. OBBBA made the TCJA brackets permanent. Tax rates aren’t scheduled to rise. The conversion logic now has to stand on its own merits — your future bracket, your RMD exposure — not on a calendar deadline.

For TSP allocation strategy in retirement after the contribution decisions are made, see G Fund vs C Fund: when each one actually wins in retirement. Federal Warrior covers the working-years federal employee perspective at Federal Warrior’s career and pay coverage ↗.