TSP Roth Conversion: Tax Rules and Examples

Federal employees with traditional Thrift Savings Plans can now convert money to a Roth TSP. This moves their future qualified growth and withdrawals into tax-free territory, but creates a substantial current-year tax bill. However, Roth TSP balances are not subject to lifetime required minimum distributions (RMDs). Here’s how the tax cost and timing can help determine whether converting supports a broader retirement strategy.

A financial advisor can help you meet all your long-term financial goals, including retirement plans.

How TSP Roth Conversions Work

A Roth in-plan conversion allows a participant to move money from a traditional TSP balance directly into a Roth. The converted amount remains invested, hence “in-plan,” within the TSP. However, any previously untaxed amount generally becomes taxable income in the year of conversion. Once converted, the IRS subjects the money to Roth tax rules, meaning qualified withdrawals can be tax-free.

An in-plan conversion differs from rolling traditional TSP assets into a Roth IRA because the money never leaves the TSP. A Roth IRA rollover moves assets to an individual retirement account outside the federal plan. This may offer a different investment menu and withdrawal rules, while still generally requiring income tax. You should add up your previously untaxed amounts before you convert them so you know what to expect.

Traditional TSP contributions generally enter the account before you’ve paid the federal income taxes, and their investment earnings also remain tax-deferred. When you convert those pretax contributions and earnings the IRS includes the taxable portion as income for that year. It does not tax any funds that it already taxed previously. After the conversion, you may withdraw future earnings tax-free if the distribution satisfies the applicable Roth qualification rules.

TSP-Specific Tax Rules for Conversions

When a traditional TSP balance contains both taxable and nontaxable money, the TSP applies the account’s taxable and nontaxable proportions to the conversion. For example, if 80% of the traditional balance is taxable and 20% represents tax-exempt contributions, an in-plan conversion generally carries the same 80/20 split.

The portion not previously subject to federal income tax is generally included in that year’s taxable income. Nontaxable amounts, such as certain tax-exempt contributions made by uniformed service members while serving in a combat zone, are not taxed again, although earnings associated with traditional tax-exempt contributions may still be taxable. The larger the share of pretax money in the account, therefore, the larger the potential income-tax bill from a conversion.

Traditional employee deferrals and their earnings are generally pretax, so converting them to Roth typically creates taxable income. Agency/Service Automatic (1%) and Matching Contributions are also traditionally deposited on a pretax basis, and the TSP permits eligible amounts from these sources to be included in Roth in-plan conversions. When converted, the TSP tracks those government contributions in separate Roth agency sources so that plan restrictions and record keeping continue to apply.

A TSP Roth in-plan conversion does not send money to the participant. So, the TSP does not withhold taxes from the converted amount. That means participants may need to cover the resulting federal and state income-tax liability with money outside the TSP or adjust estimated tax payments or paycheck withholding. The full conversion amount remains in the Roth TSP, which can preserve more retirement assets for potential tax-free growth.

There is no income limit for a TSP Roth in-plan conversion, unlike Roth IRA contributions. Conversions are available to active federal civilian and uniformed services participants as well as separated participants, allowing conversions during employment or after retirement.

Converting $300,000 at Age 50

Assume an employee converts $300,000 consisting of 80% pre-tax money and 20% nontaxable basis. The taxable conversion is $240,000, producing an estimated $57,600 federal tax at 24% plus $12,000 at an assumed 5% state rate; because TSP does not allow conversion proceeds to pay the tax, the full $300,000 remains invested in Roth while $69,600 must be covered separately. They hold the assets for 20 years, and pay the maximum capital gains rate of 20%. ¹

*All three scenarios use the same hypothetical 6% annual return; actual results vary by allocation and market performance. Tax-free treatment assumes qualified Roth distributions.

Tax Efficiency and Long-Term Planning

A Roth conversion may be more tax-efficient in years when taxable income is temporarily lower, such as after retirement but before Social Security benefits or required minimum distributions begin. Converting during these periods can allow more traditional TSP money to be taxed at relatively lower marginal rates, although a large conversion can still push part of the amount into higher tax brackets.

Using cash or other non-retirement assets to cover the conversion tax can help preserve the full amount transferred to the Roth TSP. Paying the tax from retirement assets instead may reduce the amount left to compound over time and, depending on the participant’s age and the type of distribution used, could create additional tax consequences.

Traditional TSP balances are generally subject to required minimum distributions once the participant reaches the applicable RMD age, while Roth TSP balances are not subject to lifetime RMDs for the account owner. Gradually converting traditional assets before RMDs begin may reduce future required distributions, potentially lowering taxable retirement income and giving retirees more control over when they recognize income.

The key question is not simply whether a conversion creates taxes today, but whether paying those taxes now could reduce the household’s total lifetime tax burden. Factors such as expected retirement income, future tax rates, Social Security taxation, Medicare premium surcharges and the size of future RMDs can all affect the calculation.

Bottom Line

A TSP Roth conversion can help federal employees and uniformed service members trade a tax bill today for the potential benefits of tax-free qualified withdrawals and no lifetime RMDs from the Roth TSP. Whether converting makes sense depends on factors such as current and future tax rates, available funds to pay conversion taxes, retirement timing and the mix of taxable and nontaxable money in the account. A financial advisor may be able to help you model different conversion amounts and years to determine how the strategy may affect lifetime taxes and retirement income.

Tips on Saving for Retirement 

• A financial advisor can help you create a full retirement plan and help you with a roadmap to get you to retirement. Finding a financial advisor doesn’t have to be hard. SmartAsset’s free tool matches you with vetted financial advisors who serve your area, and you can have a free introductory call with your advisor matches to decide which one you feel is right for you. If you’re ready to find an advisor who can help you achieve your financial goals, get started now.
• Saving for your retirement is one of the most important parts of staying financially healthy. While it helps to have a savings fund for emergencies, the later years when you won’t be working also need to be taken care of. This is why it’s important to maximize your 401(k) or TSP when you can. Contribute as much as you safely can and take advantage of employer matching programs.

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