TSP + Roth IRA 2026: The $3,000/Year Tax Move Most Feds Miss

Last Updated: May 3, 2026 Reading Time: 12 min

A married couple, both 65, retires with $200,000 in total annual income. They draw all of it from a fully-funded FERS pension, Social Security, and a $1.5 million traditional TSP. They pay $23,964 in federal tax. The same couple, same income, same investments, who funded a modest Roth IRA alongside their TSP across their working years, draws 80% from the TSP and 20% from the Roth IRA. They pay $20,884. That is $3,080 a year, every year, for the rest of their lives. Across a 25-year retirement at 6% growth, the gap compounds to roughly $169,000 in after-tax wealth. The Roth IRA contribution that produced it cost no more than the TSP contribution it sat alongside. The only difference was tax diversification.

Key Takeaways

• A Roth IRA funded alongside your TSP saves federal retirees $480 to $3,080 a year in federal tax, depending on income tier (FedTools 2026 analysis using 2026 IRS brackets).
• Qualified Roth IRA distributions do not count toward MAGI, so they are invisible to IRMAA (the Medicare surcharge that costs single retirees $974 to $2,297 per year per Tier).
• Roth TSP no longer has lifetime RMDs (SECURE 2.0, effective January 2024), but Roth IRA still wins on investment flexibility, withdrawal control, and spousal inheritance (a surviving spouse can roll inherited Roth IRA assets into their own).
• 2026 limits: TSP $24,500 (under 50) up to $35,750 (ages 60 to 63); Roth IRA $7,500 (under 50), $8,600 (50+). The two limits are independent.
• Mandatory Roth catch-up rule (2026): if your 2025 W-2 Box 3 wages exceeded $150,000, all TSP catch-up contributions must go to Roth TSP. (The original SECURE 2.0 $145,000 threshold is now indexed.)

The Three-Source Tax Problem at Retirement

Most federal employees plan for retirement income but do not plan for retirement tax. Three sources stack on top of each other when you stop working.

Your FERS pension is fully taxable as ordinary income. There is no exclusion, no preferential rate, no MAGI adjustment.

Your Social Security benefit is partially taxable up to 85% based on provisional income. The 85% threshold ($34,000 single, $44,000 MFJ) has not been inflation-adjusted since 1984. Almost every modern federal retiree hits 85% SS taxability.

Your traditional TSP generates Required Minimum Distributions starting at age 73. A $500,000 traditional TSP at age 73 produces about $18,868 in mandatory income in the first year. A $1 million balance produces about $37,735. You cannot opt out, defer, or smooth.

These three streams stack. They feed AGI. AGI determines federal tax bracket, Social Security taxability tier, and IRMAA. If your retirement income comes only from these three sources, you have no lever to pull when one number pushes you across a tier line. A Roth IRA is the lever.

The Original Data: Tax Savings by Income Tier

Below is the math, run through 2026 IRS brackets, 2026 standard deductions for a couple both 65+, and 2026 IRMAA schedules. Strategy A draws all retirement spending (beyond pension and SS) from a traditional TSP. Strategy B draws 80% from TSP and 20% from a Roth IRA. The Roth dollars are invisible to MAGI, provisional income, and federal tax.

Total Retirement Income	Strategy A: 100% Traditional TSP	Strategy B: 80% TSP + 20% Roth IRA	Annual Savings
$75,000	$3,704 federal tax	$3,224 federal tax	$480
$100,000	$6,800 federal tax	$5,864 federal tax	$936
$125,000	$9,704 federal tax	$8,576 federal tax	$1,128
$150,000	$13,624 federal tax	$11,384 federal tax	$2,240
$200,000	$23,964 federal tax	$20,884 federal tax	$3,080

These are MFJ numbers. Single filers save more, because the 2026 single IRMAA threshold ($109,000 MAGI) triggers earlier than the MFJ threshold ($218,000). A single GS-13 retiree at the $125,000 tier in Strategy A also pays an extra $974 to $1,949 a year in IRMAA surcharges, on top of the federal tax difference shown above. Strategy B usually keeps single filers under the IRMAA cliff.

The compounding effect is substantial. At $2,500 a year in tax savings invested at 6%, the Roth bucket's tax efficiency generates roughly $92,000 in additional after-tax wealth over 20 years, before any difference in investment return. The Roth IRA contribution that produced the savings cost the same as a TSP contribution would have.

Methodology: 2026 federal tax brackets (MFJ), 2026 standard deduction ($32,200 base + $3,300 senior add-on for couple both 65+), 2026 Social Security taxability formula, 2026 IRMAA tier schedule per CMS. Federal tax only; state tax varies. Source: FedTools 2026 Tax-Diversification Analysis.

2026 Limits: TSP and Roth IRA Are Independent

The two limits do not interact. You can max one without affecting the other.

Account	Under 50	50 to 59 or 64+	Ages 60 to 63
TSP (elective deferral + catch-up)	$24,500	$32,500 ($24,500 + $8,000 catch-up)	$35,750 ($24,500 + $11,250 super catch-up)
Roth IRA	$7,500	$8,600	$8,600

Sources: TSP Bulletin 25-3 / IRS Notice 2025-67 (TSP); IRS IR-2025-244 (Roth IRA, November 2025).

The 2026 Roth IRA phase-out: $153,000 to $168,000 (single), $242,000 to $252,000 (married filing jointly). Above the upper limits, no direct contribution is allowed, but the backdoor remains open at any income.

Where most federal grades land:

• GS-9 to GS-12 (single): Generally below the phase-out. Direct Roth IRA contribution available.
• GS-13 to GS-15 (single): Often in or above the phase-out. Calculate your MAGI after maxing traditional TSP first. A GS-14 at $155,000 base who maxes traditional TSP brings MAGI to around $130,500, well below the threshold.
• GS-14 / 15 / SES (MFJ): Usually well above the $252,000 ceiling. Backdoor Roth required.

If you assumed you earn too much for a Roth IRA, run your actual MAGI before giving up. Traditional TSP contributions reduce MAGI dollar for dollar.

The Mandatory Roth Catch-Up Rule

If you are 50 or older AND your 2025 W-2 Box 3 wages (Social Security wages, not taxable wages) exceeded $150,000, all of your 2026 TSP catch-up contributions must go to Roth TSP. The standard catch-up is $8,000. The super catch-up (ages 60 to 63) is $11,250. Both apply.

The threshold was $145,000 when SECURE 2.0 was originally enacted. It is indexed for inflation. The 2026 number is $150,000. Some older guides still cite $145,000, which is now wrong. Check Box 3 of your 2025 W-2 to know your status.

The mandatory Roth catch-up is sometimes received as a punishment, but it is the opposite. It forces high-earning federal employees into Roth diversification at exactly the wrong time to ignore it: the final years before retirement. Every Roth dollar contributed in your peak earning years becomes IRMAA-invisible income at age 73 and beyond.

Roth TSP vs Roth IRA: What's the Same, What's Different

Both are tax-free at qualified withdrawal. Both have no lifetime RMDs for the original owner since SECURE 2.0 took effect January 1, 2024. The remaining differences are not trivial.

Feature	Roth TSP	Roth IRA
2026 contribution limit	$24,500 (shared with traditional TSP)	$7,500 ($8,600 age 50+)
Income limit for contribution	None	$153K–$168K (single); $242K–$252K (MFJ)
Lifetime RMDs (owner)	None (since 2024)	None
Withdrawal of contributions only	Proportional rules apply	Yes, anytime, no tax or penalty
Investment options	G/F/C/S/I funds + L Funds + Mutual Fund Window	Unlimited
Withdrawal ordering	Proportional from all funds	Choose any fund, any amount
Spouse rollover at death	Spouse can roll to own Roth IRA (no RMDs)	Same
G Fund access	Yes (a unique advantage)	No

Common misconception to retire: "Roth TSP has RMDs so the Roth IRA wins on RMDs." That was true before 2024 and is not true now. SECURE 2.0 Section 325 eliminated lifetime RMDs on Roth balances inside 401(k)s, 403(b)s, and the TSP, effective for tax years 2024 onward. The Roth IRA still wins, but on different grounds: investment flexibility, the ability to withdraw contributions without touching earnings, and ordering control over which assets you draw down first.

For most federal employees in the accumulation phase, Roth TSP and Roth IRA are complementary, not competitors.

IRMAA: The Invisible Cost of a 100% Traditional TSP

IRMAA stands for Income-Related Monthly Adjustment Amount. It is an extra premium charged on Medicare Part B and Part D for higher-income beneficiaries, based on MAGI from your tax return two years prior. Your 2024 income determines your 2026 IRMAA. You cannot fix a bad year retroactively.

2026 IRMAA thresholds and surcharges (per person, per month):

Tier	Single MAGI	MFJ MAGI	Part B Premium	Part B Surcharge	Annual Cost (Single)
No surcharge	≤$109,000	≤$218,000	$202.90	$0	$0
Tier 1	$109,001–$137,000	$218,001–$274,000	$284.10	$81.20	$974
Tier 2	$137,001–$171,000	$274,001–$342,000	$405.80	$202.90	$2,435
Tier 3	$171,001–$205,000	$342,001–$410,000	$527.50	$324.60	$3,895
Tier 4	$205,001–$499,999	$410,001–$749,999	$649.20	$446.30	$5,356
Tier 5	$500,000+	$750,000+	$689.90	$487.00	$5,844

Add Part D surcharges of $14.50 to $91.00 per month per Tier. For a married couple where both are on Medicare, multiply by 2.

Roth IRA distributions are excluded from MAGI. They cannot trigger an IRMAA tier and they cannot push you across one. Traditional TSP withdrawals count fully. A retiree with $108,000 of MAGI in Strategy A who would have crossed into Tier 1 by drawing $5,000 more from traditional TSP can take that same $5,000 from a Roth IRA and stay clean.

The two-year lookback means the planning window is your working years, not your retirement years. By age 65 the Roth IRA balance you have is the buffer you have. Build it now.

Social Security Taxability: How Roth Changes the Formula

Social Security provisional income equals your AGI plus 50% of your SS benefit. The thresholds (frozen since 1984):

• Below $25,000 single / $32,000 MFJ: 0% of SS taxable
• $25,000 to $34,000 single / $32,000 to $44,000 MFJ: up to 50% of SS taxable
• Above $34,000 single / $44,000 MFJ: up to 85% of SS taxable

Traditional TSP withdrawals count fully in provisional income. Roth IRA qualified distributions do not. Every dollar you shift from traditional TSP to Roth IRA reduces provisional income by exactly $1.00, which can simultaneously: (1) reduce the percentage of SS that is taxable, (2) reduce total federal tax on what remains taxable, and (3) reduce MAGI for IRMAA.

A single GS-13 retiree, age 68, with $50,000 FERS pension, $40,000 traditional TSP RMD, and $28,000 Social Security has provisional income of $104,000. That makes 85% of SS taxable ($23,800 added to AGI). Total taxable income lands at $113,800, which crosses the IRMAA Tier 1 single threshold ($109,000). They owe roughly $16,000 in federal tax plus $1,148 in IRMAA, for a total of about $17,148.

If the same retiree had built a Roth IRA across their career and now draws $8,000 from it instead of an extra $8,000 from the TSP, MAGI drops to about $105,800. IRMAA disappears. Federal tax on the smaller AGI also drops. Total annual savings: about $2,900. The Roth IRA balance needed to produce that result is small, around $80,000.

The Backdoor Roth IRA for High-Income Federal Employees

The backdoor Roth is a two-step process for anyone above the direct Roth IRA contribution limit:

1. Contribute to a non-deductible traditional IRA (no income limit; same $7,500 / $8,600 cap as direct Roth).
2. Convert that traditional IRA to a Roth IRA (no income limit on conversions).

If you have no pre-existing pre-tax traditional IRA balances, the conversion is 100% tax-free. File Form 8606 every year. Many federal employees are in a clean position because the TSP is a qualified employer plan, not an IRA, and is not counted in the pro-rata calculation.

The pro-rata trap. The IRS does not let you choose which IRA dollars you convert. It treats all your traditional IRAs as one pool. If you have $100,000 in pre-tax traditional IRA funds (from a prior rollover, a SEP-IRA, or a SIMPLE IRA) and you make a $7,500 non-deductible contribution, your conversion is calculated as $7,500 / $107,500 = 6.98% tax-free. The other 93% is ordinary income. The clean backdoor becomes a mostly-taxable conversion.

The classic federal-employee mistake: rolling traditional TSP into a traditional IRA at separation, then attempting backdoor Roth contributions in subsequent years. The TSP rollover instantly creates a pro-rata problem.

The fix: if you already have pre-tax IRA balances and want clean backdoor access, roll those balances into your TSP or a new employer's 401(k). Both accept incoming traditional IRA rollovers and remove the pre-tax dollars from the pro-rata calculation. The TSP's rollover acceptance rule is the single cleanest reverse-rollover available to federal employees.

Audience Cuts: Four Profiles, Different Priorities

GS-9 to GS-12: Start the Roth IRA Now

You are below the phase-out. Direct Roth IRA contribution is fully available at $7,500 a year ($8,600 if you turn 50 in 2026). Funding a Roth IRA for 20 years at $7,500 with 7% growth produces about $307,000 in tax-free retirement assets. The single most common mistake at this grade level is treating the TSP as the only retirement vehicle because it's automatic.

Order: 5% to TSP for the match, then max Roth IRA, then increase TSP toward the $24,500 cap.

GS-13 to GS-15 (Single): Calculate Your Real MAGI Before Backdoor

Your salary may put you over $153,000, but your MAGI after maxing traditional TSP usually does not. A GS-14 at $155,000 base who contributes $24,500 to traditional TSP has MAGI around $130,500, leaving room for a full direct Roth IRA contribution. Run the actual calculation. If still over $168,000 after TSP deduction, use the backdoor.

These earners are most exposed to IRMAA Tier 1 at retirement from RMD income. The Roth IRA is the primary lever.

Ages 50 to 59 or 64+: Watch the Mandatory Roth Catch-Up

If your 2025 Box 3 W-2 was over $150,000, your $8,000 catch-up must go to Roth TSP in 2026. After that, also fund a Roth IRA ($8,600) directly or via the backdoor. The mandatory Roth catch-up is forcing tax diversification on the people who need it most: high earners with the largest traditional TSP balances heading into RMD years.

Ages 60 to 63: Use the Super Catch-Up Window

The SECURE 2.0 super catch-up of $11,250 (vs the standard $8,000) is available only at ages 60 to 63. Total TSP contribution potential: $35,750 a year. If your Box 3 wages exceed $150,000, the entire $11,250 catch-up goes to Roth TSP. Across the four years, that is $13,000 in extra Roth TSP contributions vs the standard catch-up, plus growth.

Spousal angle. A non-working spouse can still receive a Roth IRA contribution through a spousal IRA. For couples where one earner makes $150,000+, the working spouse can fund $8,600 to a spousal Roth IRA AND $8,600 to their own backdoor Roth, totaling $17,200 a year in new Roth IRA contributions while the second spouse is retired or not working.

Run Your Own Numbers Before You Retire

Open the TSP Growth & Withdrawal Calculator and project your traditional TSP balance at age 73. Divide that balance by 26.5 (the IRS Uniform Lifetime Table factor at 73). That is your first-year RMD. Add it to your projected FERS pension and 85% of your projected Social Security. If the total is above $109,000 (single) or $218,000 (MFJ), IRMAA is a near-certainty without a Roth strategy.

For deeper TSP context (allocation, withdrawal, in-plan conversion), see our TSP Guide 2026, our TSP vs IRA Rollover Decision blog (sister piece on what to do with the TSP at retirement), our TSP Roth In-Plan Conversion Guide, and the SECURE 2.0 Mandatory Roth Catch-Up explainer. For full FERS context, see our FERS Retirement Guide. For the survivor side of TSP planning (the BPA second-generation trap), see our Federal Survivor Benefits guide.

Project your retirement income stack →

Frequently Asked Questions

Can I contribute to both the TSP and a Roth IRA in the same year?

Yes. The TSP and a Roth IRA are completely separate accounts with separate limits. In 2026, you can contribute up to $24,500 to your TSP and another $7,500 to a Roth IRA ($8,600 if you are 50 or older), as long as your income is below the Roth IRA phase-out. The two limits are independent.

Do Roth TSP and Roth IRA give the same tax advantages?

Mostly yes, but not entirely. Both produce tax-free qualified withdrawals, and both are now exempt from lifetime RMDs for the original owner (Roth TSP RMDs were eliminated effective January 1, 2024 by SECURE 2.0). The Roth IRA still wins on three things: you can withdraw your contributions (not earnings) anytime without tax or penalty, you can invest in any fund anywhere, and your spouse can roll inherited Roth IRA assets into their own Roth IRA without RMDs.

Does Roth IRA income affect Medicare IRMAA surcharges?

No. Qualified Roth IRA distributions are not included in Modified Adjusted Gross Income, so they are invisible to the IRMAA formula. Traditional TSP withdrawals count fully toward MAGI and can push a single retiree across the 2026 IRMAA threshold of $109,000, costing $974 to $2,297 per person per year in extra Medicare premiums. A Roth IRA balance gives you a withdrawal source that does not feed the formula.

What is the Roth IRA income limit for federal employees in 2026?

For 2026, the phase-out begins at $153,000 (single) or $242,000 (married filing jointly). Above $168,000 single or $252,000 MFJ, you cannot make a direct Roth IRA contribution. Important: traditional TSP contributions reduce your MAGI dollar for dollar. A GS-14 earning $155,000 who maxes traditional TSP ($24,500) has MAGI of around $130,500, well below the $153,000 phase-out. Calculate your actual MAGI before assuming you cannot contribute directly.

What is the backdoor Roth IRA and can federal employees use it?

The backdoor Roth is a two-step process: contribute to a non-deductible traditional IRA (no income limit), then immediately convert to a Roth IRA (no income limit on conversions). Federal employees are well-positioned for it because the TSP is not an IRA and is not counted in the pro-rata calculation. As long as you have no pre-existing pre-tax traditional IRA balances, the conversion is fully tax-free. File Form 8606 every year. Warning: rolling your TSP into a traditional IRA after separation creates a pro-rata problem for future backdoor Roths.

Should I max my TSP first or start a Roth IRA first?

The recommended order is: contribute 5% to TSP to capture the full agency match (this is a 100% immediate return and cannot be beaten), fund your Roth IRA up to the annual limit ($7,500), then max remaining TSP elective deferrals up to the $24,500 cap. The Roth IRA gets priority over the remaining TSP elective contribution because it provides tax diversification the TSP cannot.

How does the mandatory Roth catch-up rule work in 2026?

If you are 50 or older AND your 2025 W-2 Box 3 (Social Security wages) was above $150,000, all of your 2026 catch-up contributions must go to Roth TSP. The threshold was originally $145,000 in the SECURE 2.0 statute, but it is indexed for inflation. The 2026 indexed amount is $150,000. The standard catch-up is $8,000. The super catch-up for ages 60 to 63 is $11,250. Both go to Roth if you cross the wage threshold.

How does Social Security taxability change with Roth IRA withdrawals?

Social Security taxation is based on provisional income, which equals your AGI plus 50% of your SS benefit. Traditional TSP withdrawals count as AGI. Roth IRA qualified distributions do not. Shifting $10,000 of annual income from traditional TSP to a Roth IRA can move you from the 85% SS taxability tier to the 50% tier. The 85% threshold is $34,000 (single) or $44,000 (MFJ). These thresholds have not been adjusted for inflation since 1984.

When does IRMAA become a real risk for federal retirees?

A single retiree with a traditional TSP above $500,000 at age 73 is at high risk of IRMAA Tier 1 from RMDs alone. A $500,000 traditional TSP generates an RMD of about $18,868 in the first year, which combined with a modest FERS pension and Social Security pushes total MAGI over $109,000. For married couples, the trigger threshold is $218,000 MFJ MAGI, but a combined traditional TSP above $1.5 million at age 73 will hit it for most couples. Roth balances built during your working years are the buffer.

Related Resources

• TSP Growth & Withdrawal Calculator: Project your TSP balance at age 73 and your first-year RMD
• TSP Guide 2026: Pillar guide on TSP allocation, fees, and withdrawals
• TSP vs IRA Rollover Decision 2026: What to do with your TSP at retirement (sister piece on rollover, not concurrent contribution)
• TSP Roth In-Plan Conversion Guide 2026: How to convert traditional TSP to Roth TSP without leaving the plan
• SECURE 2.0 Mandatory Roth Catch-Up 2026: The $150,000 Box 3 threshold rule explained
• Federal Survivor Benefits Planning 2026: Roth IRA inheritance vs Roth TSP BPA, and the second-generation tax trap
• FERS Retirement Guide 2026: Foundational FERS pension context

Sources: TSP Bulletin 25-3 / 2026 Limits · IRS IR-2025-244 (2026 IRA limits) · TSP.gov SECURE 2.0 Page (Roth TSP RMD elimination) · Tax Foundation 2026 Federal Tax Brackets · Income Laboratory 2026 IRMAA Guide · IRS Publication 590-A · SSA Provisional Income Rules · MyFederalRetirement: $150K Mandatory Roth Threshold · MyFederalRetirement: No Lifetime RMD for Roth TSP