neo@web:~/guides $ cat tsp-funds-explained
The TSP has five individual funds: G holds special-issue Treasury securities and cannot lose money; F tracks the Bloomberg U.S. Aggregate Bond Index; C tracks the S&P 500; S tracks small and mid-size U.S. companies through the Dow Jones U.S. Completion Index; I tracks international stocks through the MSCI ACWI IMI ex USA ex China ex Hong Kong Index. The eleven Lifecycle funds are pre-mixed portfolios of these five that grow more conservative as their target date nears. You can hold a single L Fund for your entire account, or build your own mix from the five.
Every TSP investment choice comes down to five letters. The Thrift Savings Plan offers exactly five individual funds, and everything else it sells, including the Lifecycle funds, is a recipe made from those five ingredients. There is no menu of hundreds of mutual funds to sort through, which is both the limitation and the appeal of the plan.
This guide explains each fund the way you would explain it to a coworker: what it holds, what kind of risk it carries, and where it fits. No return figures are quoted here, because any specific number goes stale fast. The TSP publishes historical returns for every fund at tsp.gov, and you should check the current figures there before making changes.
The G Fund is the one investment in the world that no private investor can buy. It holds short-term U.S. Treasury securities that are issued only for the TSP, and the U.S. government guarantees the principal. That means the G Fund cannot have a losing month. Your balance in the G Fund only goes up, by the amount of interest earned.
The interest rate tracks longer-term Treasury yields, so it pays more like a long-term bond while carrying no risk of principal loss. The catch is inflation risk. In years when prices rise faster than the G Fund's interest rate, your purchasing power shrinks even though your balance never falls. Over decades, the G Fund has the lowest return of the five funds.
The G Fund's best role is as a shock absorber: money you will need soon, or the stabilizing slice of a portfolio that is mostly in stocks. Participants who keep their entire career's savings in the G Fund are choosing certainty of balance over growth, and that tradeoff compounds against them over thirty years.
The F Fund is the TSP's bond fund. It tracks the Bloomberg U.S. Aggregate Bond Index, a broad basket of government, corporate, and mortgage-backed bonds traded in U.S. markets. When you own the F Fund, you are lending money to governments and companies and collecting the interest.
Bonds are calmer than stocks but not risk-free. When interest rates rise, existing bonds with lower rates become less attractive, so bond prices fall and the F Fund can lose money in a given year. When rates fall, the reverse happens. Over long periods the F Fund has returned more than the G Fund, with more wobble along the way.
In a portfolio, the F Fund plays the classic bond role: income and a cushion when stocks fall. Many participants pair it with the C and S funds so that one part of the account zigs while the other zags.
The C Fund tracks the S&P 500, an index of the 500 largest U.S. companies. This is the fund most federal employees mean when they say their TSP is "in the market." The S&P 500 represents roughly four-fifths of the total value of the U.S. stock market, so the C Fund is a bet on large American business as a whole.
Stocks deliver the highest long-run returns of any TSP asset class, and the C Fund has historically been the strongest performer of the five funds over multi-decade stretches. The price is volatility: in a bad year the C Fund can drop hard, and it has had stretches of several years with little to show. Time horizon is what makes the C Fund work. With twenty or thirty years, the down years have historically been overwhelmed by the up years. With two years, a market drop can land right when you need the money.
For most participants with a long career ahead, the C Fund is the core holding. Everything else in the TSP is either a complement to it or a refuge from it.
The S Fund tracks the Dow Jones U.S. Completion Total Stock Market Index, which holds the small and mid-size U.S. companies that are not in the S&P 500. Think of it as the rest of the American stock market after the C Fund takes the biggest 500 names. Add the C Fund and the S Fund together and you own essentially the entire U.S. stock market.
Smaller companies have higher growth potential than large established ones, and they also fail more often, so the S Fund is more volatile than the C Fund. It tends to outperform large caps in some decades and lag in others. Its value in a portfolio is diversification: there are long stretches when small caps lead and the C Fund alone would have missed it.
A common pairing is roughly four parts C Fund to one part S Fund, which approximates the total U.S. market. That ratio is a starting point for your own research, not a recommendation.
The I Fund tracks the MSCI ACWI IMI ex USA ex China ex Hong Kong Index, a basket of stocks from developed markets outside the United States. It is the TSP's only direct exposure to the rest of the world's economies.
International stocks add a genuine diversifier: there are long periods when foreign markets outperform the U.S., and holding them smooths the ride of a U.S.-only portfolio. The extra risks are currency movement, which can help or hurt returns when translated back to dollars, and the political and economic risks of foreign markets.
The I Fund is the most misunderstood of the five, partly because its benchmark changed over the years. What matters today is simple: it is your non-U.S. stock allocation, and a globally diversified portfolio includes some of it.
If picking five funds and rebalancing them sounds like a chore, the TSP built the answer: eleven Lifecycle funds, each a professionally managed mix of the five individual funds. You pick the fund whose target date is near your planned retirement, put your whole account in it, and the TSP does the rest.
Every quarter, each L Fund's target allocation shifts a little more conservative as its target date approaches, moving from stock-heavy to bond-and-G-Fund-heavy along what professionals call a glide path. The fund rebalances to its target allocation every trading day, which in effect buys low and sells high across the five ingredients. When a fund reaches its target date, it folds into the L Income Fund, the most conservative of the series, designed for people already drawing on their accounts.
The L Funds were designed to hold your entire balance. Mixing an L Fund with individual funds on the side usually just muddies the allocation the professionals set. One caution from TSP officials over the years: the most common mistake is pairing an L Fund with a heavy G Fund position, which double-counts conservatism and drags down long-run growth.
Start with your time horizon. Money you need within a few years belongs in the G Fund or the L Income Fund, because a market drop right before you spend the money is the one risk you cannot recover from. Money you will not touch for twenty years can carry mostly stocks, because time has historically absorbed the down years.
Next, be honest about your temperament. The mathematically optimal portfolio is worthless if you sell it in a panic during the first 20% drop. An allocation you can hold through a bad year beats a theoretically better one you abandon.
Then keep two mechanics in mind. First, fees: the TSP's expense ratios are published yearly and sit far below typical 401(k) fund fees, so cost is one thing you do not need to optimize. Second, trading limits: TSP rules allow only two interfund transfers per calendar month, with additional moves restricted to the G Fund, so the plan is built for long-term allocations, not frequent trading.
If you were automatically enrolled and never chose an allocation, check where your money actually is. Since 2015, new participants default into an age-appropriate L Fund rather than the G Fund, but anyone enrolled earlier who never chose may still be sitting entirely in G. That single default has cost some participants years of growth, and it takes minutes to fix at tsp.gov.
Run your own numbers with our TSP growth calculator, which projects your balance under your own assumed return and shows the agency match dollars separately. Then confirm the current fund facts at tsp.gov before you move money.
Data current as of October 2026. Source: Thrift Savings Plan (tsp.gov).