Roth vs. Traditional TSPThe real question isn’t taxes. It’s flexibility.

Imagine you are a farmer with four bags of seed and four empty fields. Each bag of seed is planted and grows into one field of crops.

At some point, taxes must be paid. The only question is whether you pay the tax on the seed before it is planted or on the crops after they have grown.

With Roth contributions, taxes are paid first. You begin with four bags of seed but must give one bag to the IRS immediately. That leaves you with three bags to plant.

With Traditional contributions, taxes are deferred. You keep all four bags of seed and plant them.

Result: You keep 3 fields of crops. If the tax rate is the same when the money goes in and when it comes out, Roth and Traditional produce the same after-tax result.

What This Example Demonstrates

If the tax rate is identical when the contribution is made and when the money is withdrawn, the after-tax outcome is identical. The key question is therefore not whether the account is Roth or Traditional. The key question is:

If your marginal income-tax rate is expected to be lower in retirement, Traditional contributions may have the advantage. If your marginal income-tax rate is expected to be higher in retirement, Roth contributions may have the advantage. This is why many Roth versus Traditional discussions focus on comparing today’s tax bracket with your expected tax bracket in retirement.

However, retirement planning is rarely that straightforward.

For Foreign Service Officers, this decision often sits alongside other moving parts: TSP balances, FSPS pension income, Social Security, possible rental income, overseas assignments, and state domicile changes. That makes the Roth-versus-Traditional question less about finding one universally correct answer and more about preserving useful options over time.

Why Tax Rates Alone Don’t Tell the Whole Story

The farmer example illustrates an important principle, but Foreign Service retirement income interacts with a variety of benefits and tax rules that can affect the value of Roth and Traditional TSP savings.

Retirement withdrawals may influence:

• Marginal tax brackets
• Social Security taxation
• Medicare IRMAA surcharges
• Required Minimum Distributions (RMDs)
• Estate and legacy planning

As taxable income rises, these interactions can reduce flexibility and limit the number of available planning options.

For many retirees, the real value of Roth savings is not avoiding income taxes in retirement. It is preserving the ability to manage taxable income when these rules begin interacting.

Most retirees will still have access to the standard deduction, and at least some income may be taxed in lower brackets than the marginal rate they faced during their working years. Those low-tax brackets represent valuable space that may be worth using.

The objective is not to put every dollar into either Roth or Traditional accounts. It is to understand how different tax buckets can work together.

A retiree with both Traditional and Roth assets can choose where income comes from each year. Traditional withdrawals can be used to fill available deductions and lower tax brackets, while Roth withdrawals can provide additional spending without increasing taxable income.

In many cases, the ability to control when and how income is recognized may be more valuable than maximizing either Roth or Traditional contributions in isolation.

Required Minimum Distributions (RMDs)

Traditional TSP balances and other tax-deferred retirement accounts generally require withdrawals later in life, whether the money is needed to pay for expenses or not. Either way, a portion of those savings must be distributed from the account. Under current tax law, Traditional TSP balances become subject to Required Minimum Distributions (RMDs) beginning at age 75 for individuals born in 1960 or later.

These required withdrawals:

• Increase taxable income
• Reduce control over withdrawal timing
• May push income into higher tax brackets
• Can trigger additional taxation elsewhere

Roth TSP balances are currently not subject to RMDs during the original owner’s lifetime, allowing greater control over when assets are used.

Social Security Taxation

Many retirees assume Social Security benefits are tax-free. In reality, the taxable portion of Social Security is up to 85% and depends on other sources of income. As Traditional TSP withdrawals increase, they can cause a larger portion of Social Security benefits to become taxable.

In effect:

1. The withdrawal itself is taxable.
2. The withdrawal may cause additional Social Security income to become taxable.
3. The actual tax impact may be larger than expected, a phenomenon often referred to as the “Social Security tax torpedo.”

Qualified Roth withdrawals do not create this effect because they are not included in taxable income.

Medicare IRMAA Surcharges

Medicare premiums are based on taxable income. Higher taxable income can trigger Income-Related Monthly Adjustment Amount (IRMAA) surcharges that increase Medicare Part B and Part D premiums.

Traditional TSP withdrawals can contribute to those thresholds. Qualified Roth withdrawals do not.

As a result, two retirees spending the same amount of money may pay different Medicare premiums depending on where their retirement paycheck comes from.

State Tax Planning

Traditional contributions defer not only federal income taxes, but state income taxes as well.

Those deferred taxes will be recognized when funds are withdrawn or converted. As a result, the state in which you are domiciled at the time of withdrawal may ultimately determine how much state tax is paid on those withdrawals.

This consideration can be particularly relevant for Foreign Service Officers, who often establish ties to multiple states over the course of a career marked by frequent relocations, overseas assignments, and domestic tours.

For example, an individual may earn income while domiciled in a state with relatively high income taxes but later retires to a state with lower income taxes or no state income tax at all. In that situation, deferring taxation through Traditional contributions may allow some retirement savings to be taxed under a more favorable state tax regime.

Conversely, an individual who expects to retire in a state with higher income taxes than their current state may place greater value on paying taxes today through Roth contributions.

While federal tax considerations often receive the most attention, state tax treatment can also influence the long-term value of Traditional and Roth savings. For individuals who expect their state of domicile to change over time, the ability to defer the state tax decision until retirement may create additional planning opportunities.

Tax Bracket Management

Many retirees receive income from several different sources:

• Foreign Service Pension System (FSPS)
• Social Security
• Taxable brokerage accounts
• Rental income
• Interest and dividends

These income sources often fill portions of the lower income-tax brackets before discretionary TSP withdrawals begin. Additional Traditional withdrawals are stacked on top of existing income and may be taxed at increasingly higher marginal rates.

Roth withdrawals can provide spending power without increasing taxable income, creating flexibility for:

• Large purchases
• Home repairs
• Medical expenses
• Market downturns
• Tax law changes

Capital Gains Harvesting

Roth withdrawals provide another form of tax flexibility that is often overlooked. Because qualified Roth withdrawals do not increase taxable income, they do not increase either ordinary income tax rates or long-term capital gains tax rates. This can create opportunities to harvest long-term capital gains at favorable tax rates.

For retirees who maintain taxable brokerage accounts, lower taxable income may allow some or all long-term capital gains to fall within the 0% capital gains tax bracket.

A retiree may be able to fund spending needs from Roth assets while realizing gains from appreciated investments in a taxable account. Because the Roth withdrawal does not increase taxable income, the gain may still qualify for the 0% long-term capital gains rate.

Potential benefits include:

• Repositioning investments with little or no federal tax cost
• Increasing cost basis in taxable accounts
• Reducing future capital gains exposure
• Improving long-term tax efficiency

The specific capital gains thresholds change periodically and should be verified using current IRS guidance. However, the planning opportunity remains the same:

The Value of Tax Diversification

Many discussions frame Roth versus Traditional as a prediction about future tax rates. A more complete framework is:

A retiree with only Traditional assets may have limited control over taxable income. A retiree with only Roth assets may have paid more tax than necessary during working years. A combination of Traditional and Roth TSP balances creates tax diversification, allowing withdrawals to be sourced strategically based on income needs and tax circumstances.

For example, during a year with unusually low taxable income, a retiree may choose to:

• Withdraw additional Traditional TSP funds
• Complete a Roth conversion
• Intentionally fill lower tax brackets

During years with higher taxable income, that same retiree may rely more heavily on Roth assets to avoid increasing tax exposure. This flexibility allows retirees to make decisions based on current circumstances rather than being forced into a single tax outcome.

That flexibility can be especially valuable during years when income is unusually low, creating opportunities to convert Traditional assets to Roth at favorable tax rates.

What if Future Tax Rates Rise?

One of the most common arguments in favor of Roth contributions is the belief that tax rates will be higher in the future. That may prove true. It may also prove false.

The challenge is that no one can predict with certainty how the tax code will evolve over coming decades. Even if tax rates increase, it is impossible to know today which rates will change, by how much, and for whom. Future tax changes could include:

• Higher marginal tax rates across all brackets
• Increases concentrated in higher-income brackets
• Additional tax brackets layered on top of existing rates
• Changes to deductions, exemptions, or credits
• Changes to the taxation of retirement income, Social Security, or capital gains

There are just too many variables and unknowns for future tax rates alone to serve as the cornerstone of a retirement savings strategy.

For that reason, rather than trying to predict future tax law, I believe there is value in maintaining flexibility through tax diversification. Just as investment diversification reduces reliance on any single market outcome, tax diversification reduces reliance on any single future tax environment.

The Real Decision

The Roth decision is often presented as a prediction about future tax rates, but for many Foreign Service families it is also a question of control.

Traditional savings maximize tax deferral today. Roth savings can preserve options tomorrow. The more retirement income sources you expect to have, the more valuable flexibility can become.

The objective is not necessarily to accumulate only Roth assets or only Traditional assets. It is to build a mix of taxable, tax-deferred, and tax-free resources that allows you to manage taxable income when it matters most.

A well-diversified retirement portfolio does not just provide investment diversification. It also provides tax diversification, creating additional options as tax laws, spending needs, and retirement income sources evolve over time.

After all, paying the tax on the seed allows the crop to grow freely.