TSP Traditional vs Roth: How Each Affects Your Take-Home Pay
Every TSP contribution you make is either Traditional (pre-tax) or Roth (after-tax). This choice directly affects your take-home pay today and your tax burden in retirement. Here is exactly how each option works.
The Core Difference
| Feature | Traditional TSP | Roth TSP |
|---|---|---|
| Tax treatment now | Pre-tax — reduces current federal taxable income | After-tax — does NOT reduce current taxable income |
| Tax treatment in retirement | Withdrawals taxed as ordinary income | Qualified withdrawals are tax-free |
| Reduces FICA wages? | No | No |
| Government match | Same formula (always goes to Traditional) | Same formula (always goes to Traditional) |
Take-Home Pay Impact: A Real Example
Consider a GS-12 Step 5 employee in the Rest of U.S. locality area (annual salary $101,443), filing Single, FERS-FRAE, with $180 biweekly FEHB, in a no-income-tax state:
| Item | 5% Traditional TSP | 5% Roth TSP |
|---|---|---|
| Gross biweekly | $3,901.65 | $3,901.65 |
| TSP deduction | $195.08 | $195.08 |
| Federal tax withholding | $398.45 | $441.37 |
| Net biweekly pay | $2,671.75 | $2,628.83 |
| Difference | $42.92 more per paycheck with Traditional | |
With Traditional TSP, you take home about $43 more per paycheck because the contribution reduces your taxable income today. With Roth, you pay more tax now but your TSP withdrawals in retirement will be tax-free (after meeting qualifying conditions).
Important: Regardless of whether you choose Traditional or Roth for your own contributions, the government matching contributions always go into your Traditional TSP balance. This means even an all-Roth contributor will have some Traditional balance from the match.
When Traditional Makes More Sense
Traditional TSP tends to be advantageous when you expect your tax rate in retirement to be lower than your current marginal rate. This is common for employees in higher GS grades (GS-13 through GS-15) who are currently in the 22% or 24% federal bracket but expect lower income in retirement.
When Roth Makes More Sense
Roth TSP tends to be advantageous when you expect your tax rate in retirement to be the same or higher. This may apply to earlier-career employees at lower grades (GS-5 through GS-9) who are currently in the 10% or 12% bracket and expect their income (and tax rates) to rise over time. Roth is also valuable for tax diversification in retirement.
SECURE 2.0: Mandatory Roth Catch-Up (2026)
Starting January 1, 2026, employees whose prior-year FICA wages exceeded $150,000 must make catch-up contributions as Roth. This is not optional—it is required by SECURE 2.0 Act §603. Many GS-14 and GS-15 employees in DC, SF, NY, and other high-locality areas will be affected.
Sources & Legal Citations
TSP Traditional/Roth: TSP.gov
Government Match: 5 U.S.C. §8432(c)
Premium Conversion (FEHB pre-tax): 26 U.S.C. §125
Mandatory Roth Catch-Up: SECURE 2.0 Act §603
Federal Tax Brackets 2026: IRS Rev. Proc. 2025-32; P.L. 119-21 (OBBBA)
Detailed Tax Bracket Analysis
The Roth vs. Traditional decision fundamentally comes down to tax rate comparison: your marginal tax rate now versus your expected effective tax rate in retirement. Here is how common GS salary levels map to 2026 federal tax brackets for single filers after standard deduction and typical pre-tax deductions:
GS-7 Step 1 DC ($68,405): After FERS, FEHB, and standard deduction, taxable income falls in the 12% bracket. At this rate, the tax savings from Traditional TSP are modest. Roth may be preferable since your tax rate is likely to rise with promotions.
GS-12 Step 5 DC ($102,415): After deductions, you are likely in the 22% bracket. Traditional saves roughly $43 per paycheck at 5% contribution. Whether to use Roth depends on your expected retirement income and tax landscape.
GS-15 Step 10 DC ($197,200, capped): You are in the 24% bracket. Traditional TSP provides substantial tax savings now. Most financial planners would suggest a significant Traditional allocation at this income level, though some Roth for tax diversification is commonly recommended.
The Tax Diversification Argument
Many federal financial planners recommend splitting contributions between Traditional and Roth to hedge against future tax rate uncertainty. Since no one can predict with certainty what tax rates will be in 20 or 30 years, having both Traditional (tax-deferred) and Roth (tax-free) buckets in retirement provides flexibility. You can draw from Traditional in low-income years and Roth in high-income years, potentially optimizing your lifetime tax burden.
The OBBBA (P.L. 119-21) permanently extended TCJA rates, but future Congresses could change rates. The current rates (10%, 12%, 22%, 24%, 32%, 35%, 37%) represent historically moderate levels. If rates increase significantly in the future, Roth contributions made today at lower rates would be more valuable.
Social Security Income Taxation
In retirement, up to 85% of your Social Security benefits may be taxable depending on your "combined income." Traditional TSP withdrawals count toward combined income; Roth TSP withdrawals do not. This means heavy Traditional TSP withdrawals in retirement could push more of your Social Security income into the taxable range. This is another argument for Roth diversification, particularly for employees who expect significant FERS pension plus Social Security income in retirement.
Required Minimum Distributions
Traditional TSP accounts are subject to Required Minimum Distributions (RMDs) starting at age 73 (under current law). Roth TSP accounts in the TSP are also currently subject to RMDs, though you can avoid this by rolling your Roth TSP into a Roth IRA after separation, which has no RMD requirement. This is a planning consideration for employees who may not need all their retirement savings immediately.
The Five-Year Rule for Roth TSP
To receive tax-free withdrawals from your Roth TSP, you must meet two conditions: you must be at least age 59½ (or disabled or deceased), and at least 5 years must have passed since January 1 of the year you made your first Roth contribution. If you start making Roth contributions at age 55, your Roth earnings will not be tax-free until you are at least 60. This five-year clock starts only once, so the earlier you make at least one Roth contribution, the better.
One Simple Framework
If you are paralyzed by the Traditional vs. Roth choice, a practical approach is to contribute enough Traditional to lower your taxable income to the bottom of your current bracket, then contribute any additional amount as Roth. This maximizes the current-year tax benefit of Traditional contributions while building a Roth balance for tax-free withdrawals in retirement. If this is too complex, a 50/50 split is a reasonable default that provides good tax diversification.
State Tax Considerations
Some states do not tax retirement income, including distributions from accounts like the TSP. If you plan to retire in a state with no income tax on retirement distributions (such as Florida, Texas, or Nevada), Traditional TSP becomes more attractive because you may pay zero state tax on withdrawals. Conversely, if you currently live in a no-income-tax state and contribute Roth, you gain no state-level tax benefit from the Roth designation since there was no state tax to avoid in the first place. Consider your likely retirement location when making the Traditional vs. Roth decision.
Federal pensions and Social Security are taxed differently by each state. Some states exempt federal pension income from state tax entirely, while others tax it fully. This adds another layer of complexity to the Roth vs. Traditional analysis. A comprehensive retirement tax projection, accounting for all income sources and your expected retirement state, provides the clearest picture.
Frequently Asked Questions
Does Roth TSP reduce my take-home pay more than Traditional?
Yes. Roth contributions are after-tax, so they do not reduce your federal taxable income. A GS-12 Step 5 employee contributing 5% Roth takes home about $43 less per paycheck than one contributing 5% Traditional, based on 2026 tax brackets.
Where does the government match go — Traditional or Roth?
Agency matching and automatic contributions always go into your Traditional TSP balance, regardless of how you designate your own contributions. Even if you contribute 100% Roth, the match is Traditional.
Can I split contributions between Traditional and Roth?
Yes. You can designate any percentage of your contribution as Traditional and the rest as Roth, as long as the combined total stays within the annual IRS limit ($24,500 in 2026, plus catch-up if eligible).
Do I have to use Roth for catch-up contributions in 2026?
Only if your prior-year FICA wages exceeded $150,000. This mandatory Roth catch-up rule took effect January 1, 2026 under SECURE 2.0 Act §603. If your wages were below $150,000, you can choose Traditional or Roth for catch-up contributions.
Does either TSP type reduce Social Security or Medicare taxes?
No. Neither Traditional nor Roth TSP contributions reduce your FICA wages. Social Security (6.2%) and Medicare (1.45%) are calculated on gross pay minus FEHB premiums only.