5 Mistakes to Avoid when Investing in the Thrift Savings Plan (TSP)

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The Thrift Savings Plan (TSP) is one of the most powerful retirement tools available to federal employees—low fees, strong fund options, and a valuable agency match for FERS participants. But power alone doesn’t guarantee a good outcome. Small, easy-to-miss mistakes can quietly cost you tens of thousands of dollars over a career.

At Government Retirement Solutions, we help federal employees and other public-sector workers with similar defined contribution plans make clearer decisions about contributions, allocation, Roth vs. Traditional, loans, and beneficiaries. A consultation—and, when it fits, a personalized Retirement Blueprint—can surface issues that are hard to spot on your own.

Here are five TSP mistakes we see often, and how to avoid them.

1. Missing Out on the Full Available Match

If you’re under FERS, your agency automatically contributes 1% of your basic pay to your TSP whether you contribute or not. On top of that, the agency matches 100% of the first 3% you contribute and 50% of the next 2%. Contribute at least 5%, and you capture the full available match—effectively another 5% of pay going into your account each pay period (1% automatic + up to 4% matching).

Contribute less than 5%, and you leave free money on the table. Here’s a simple comparison for a $100,000 salary (about $3,846.15 per pay period), showing what goes into the TSP each pay period at a 5% vs. 3% contribution rate:

That gap—about $115 per pay period—adds up to roughly $3,000 a year, or around $30,000 over 10 years, before raises or investment growth. Getting to at least 5% is one of the highest-ROI moves available in the federal benefits package.

2. Playing It Too Safe

Many employees keep a large share of their TSP in very conservative options for years—sometimes decades—because market swings feel uncomfortable. With a long time horizon, that caution can create a different kind of risk: opportunity cost. Inflation and under-allocation to growth assets can quietly shrink what your nest egg will buy in retirement.

A balanced allocation matched to your timeline, risk tolerance, and other retirement income (pension, Social Security) is usually more productive than sitting entirely on the sidelines. An experienced advisor can help you stay disciplined through volatility instead of reacting to headlines.

3. Taking a TSP Loan Without Understanding the Real Cost

TSP loans can look attractive because you’re “borrowing from yourself.” The hidden cost is often misunderstood. Loan repayments are made with after-tax dollars, and if the money came from a Traditional TSP balance, those same dollars can be taxed again when you withdraw them in retirement. You also miss the market growth those funds might have earned while they were out of the market.

There’s another hard stop: if you leave federal service with an outstanding TSP loan, you generally have about 90 days to repay the balance. If you don’t, the unpaid amount is typically treated as a taxable distribution—and if you’re under age 59½, a 10% early withdrawal penalty may apply as well. Before you borrow, run the full cost, not just the interest rate.

4. Overlooking the Roth TSP Option

Traditional TSP contributions lower your taxable income now and are taxed later in retirement. Roth TSP contributions are made with after-tax dollars, and qualified withdrawals—including earnings—can be tax-free. Unlike a Roth IRA, the Roth TSP has no income limit, so higher earners who are phased out of a Roth IRA can still use Roth inside the TSP.

Which mix is right depends on your current tax bracket, expected retirement bracket, and overall plan. GRS can model Traditional vs. Roth scenarios so you’re not guessing.

5. Forgetting to Update Your Beneficiary Designation

Your TSP does not follow your will for beneficiary purposes. Designations are made on Form TSP-3, and if you never filed one—or haven’t updated it after a life change—the TSP follows a statutory order of precedence that may not match your wishes. Marriage, divorce, a new child, or the death of a named beneficiary are all moments to review TSP-3. A five-minute update can prevent a painful surprise for the people you intend to protect.

The Bottom Line

Capturing the full match, staying appropriately invested, treating loans with caution, using Roth thoughtfully, and keeping beneficiaries current are five of the highest-leverage TSP habits we see. None of them require exotic strategies—just clarity and follow-through.