TSP funds explained: G, F, C, S, I and L Funds

How TSP investing is set up

The Thrift Savings Plan is the defined contribution plan for federal civilian employees and members of the uniformed services. In plain terms, it's the federal government's version of a 401(k). What makes it unusual is how short the menu is. Instead of dozens of actively managed mutual funds, you choose from a few broad index funds. Most of them are run by outside asset managers whose only job is to track a published benchmark as closely and cheaply as they can.

You can invest in two ways:

• Individual funds. You pick your own mix of the G, F, C, S and I Funds and decide how much goes into each.
• Lifecycle (L) Funds. You pick one target-date fund. The TSP mixes and rebalances the five individual funds for you and gets more conservative as the target date gets closer.

There's also a mutual fund window for people who want more choice. It comes with extra fees and limits, which are covered below. Most participants never need it.

G Fund: Government Securities Investment Fund

The G Fund invests in short-term U.S. Treasury securities issued specifically to the TSP. According to the Summary of the Thrift Savings Plan, it lets you earn interest rates similar to long-term government securities "with no risk of loss of principal," and the U.S. government guarantees payment of principal and interest. The rate resets monthly.

That guarantee makes the G Fund unique in the retirement world. A normal bond fund can lose value when interest rates rise. The G Fund doesn't, because its securities don't trade on the open market. Its main risk is inflation risk: over long periods, returns may only modestly beat inflation, or may fail to beat it at all. That makes it a weak engine for long-term growth for most younger investors. It works best as a stabilizer, an emergency-style reserve inside the plan, or a source of withdrawals during market downturns in retirement.

2025 total expense ratio: 0.034% (tsp.gov).

F Fund: Fixed Income Index Investment Fund

The F Fund tracks the Bloomberg U.S. Aggregate Bond Index. That broad index covers investment-grade U.S. bonds: Treasuries, government agency debt, mortgage-backed securities and corporate bonds. The F Fund pays more interest than the G Fund over time, but it carries risks the G Fund doesn't:

• Interest-rate risk. When rates rise, existing bond prices fall. Investors felt this in 2022, when the broad U.S. bond market had one of its worst years on record.
• Credit risk. A borrower could default on a scheduled payment.
• Prepayment risk. Mortgage-backed securities can be paid off early when rates fall.

Even with those risks, the F Fund has historically moved differently from stocks, so it can dampen a portfolio's swings. That's why the L Funds hold it. 2025 total expense ratio: 0.035%.

C Fund: Common Stock Index Investment Fund

The C Fund tracks the S&P 500, an index of 500 large U.S. companies (TSP Summary). It's the TSP's most popular stock fund and the one most people mean when they say "the market." The S&P 500 is weighted by market value, so its largest companies have an outsized effect on returns. In recent years that has meant heavy exposure to a handful of mega-cap technology companies.

The C Fund offers the higher long-term growth potential that comes with stocks, along with real downside. Large-company U.S. stocks have fallen more than 30% from peak to trough several times in recent decades. Its main risk is market risk, meaning stock prices fall broadly. 2025 total expense ratio: 0.035%.

S Fund: Small Cap Stock Index Investment Fund

The S Fund tracks the Dow Jones U.S. Completion Total Stock Market Index. That index holds U.S. stocks that are not in the S&P 500, which tsp.gov describes as over 3,000 small and medium-sized companies. The name "completion" is the clue: hold the C and S Funds in proportion to their market sizes and you own roughly the entire U.S. stock market.

Smaller companies have historically been more volatile than large ones. In some periods they've beaten large caps, and in others, like much of the last decade, they've trailed. The S Fund is a reasonable diversifier, but treating it as a "turbo C Fund" assumes small caps will win, and they don't always. 2025 total expense ratio: 0.051%, the highest of the core funds and still tiny by industry standards.

I Fund: International Stock Index Investment Fund

The I Fund changed in 2024. It used to track the MSCI EAFE index of developed markets. It now tracks the MSCI ACWI IMI ex USA ex China ex Hong Kong Index. The TSP completed that transition in October 2024. According to the TSP's fund information sheet, the new index had more than 5,100 companies across 44 developed and emerging-market countries as of December 31, 2025, including large, mid and small companies. It excludes the U.S., China and Hong Kong.

Besides normal stock-market risk, the I Fund carries currency risk. When the dollar strengthens, foreign returns translate into fewer dollars, and when it weakens, they translate into more. International stocks often go through long stretches of beating or trailing U.S. stocks, which is exactly why many diversified portfolios hold both. 2025 total expense ratio: 0.048%.

Side-by-side comparison

Expense ratios are 2025 totals (net administrative + investment) published on tsp.gov. Check tsp.gov for current rates of return; past performance doesn't guarantee future results.

L Funds: the TSP's target-date option

The Lifecycle Funds are pre-built portfolios of the five individual funds. As of 2026 there are eleven: L Income, L 2030, L 2035, L 2040, L 2045, L 2050, L 2055, L 2060, L 2065, L 2070 and L 2075. The number is roughly the year you expect to start withdrawing. Three features matter:

• Quarterly glide path. Every quarter, each L Fund (except L Income) shifts its target mix a little toward the G and F Funds. Over time it moves from higher risk and reward toward lower risk and reward.
• Daily rebalancing. At the end of each trading day the TSP buys and sells the underlying funds to get back to the target mix. tsp.gov describes this as effectively "buying low and selling high."
• Roll into L Income. When an L Fund reaches its target year, it closes and its money moves into L Income. In 2030, for example, L 2030 rolls into L Income.

The L Funds don't charge an extra layer of fees. Their expense ratios simply reflect the underlying funds. In 2025 those ranged from 0.035% (L Income) to 0.041% (tsp.gov). According to the TSP, L Income is designed for participants born before 1965, who are already withdrawing or who plan to begin before 2028.

New employees who don't make an investment choice are generally placed in the age-appropriate L Fund. If you have never looked at your allocation, that's probably where your money is. It isn't a bad place to be, but it's worth checking whether that fund's risk level actually fits your plans. Our guide to TSP allocation by age goes deeper.

Individual funds or an L Fund?

This is less about which is "better" and more about how you behave as an investor:

• An L Fund fits if you want a set-it-and-forget-it approach, don't want to rebalance, and are comfortable with the TSP's glide path. Its biggest advantage is behavioral: it rebalances automatically and doesn't panic.
• Individual funds fit if you want a mix that's more or less aggressive than the L Fund for your age, or you're coordinating the TSP with a pension, an IRA or a spouse's accounts. They also fit if you want to set your own bond/stock split. The trade-off is that you're responsible for rebalancing.

One common mistake is combining an L Fund with individual funds without realizing the L Fund already holds all five. That often leaves you with a different overall mix than you intended. Another mistake is chasing last year's winner. The TSP limits how often you can move money: each calendar month, your first two interfund transfers or reallocations can go to any fund, and after that you can only move money into the G Fund for the rest of the month (TSP Summary).

What about the mutual fund window?

The mutual fund window lets you invest part of your TSP in thousands of outside mutual funds. Per tsp.gov, your initial transfer must be at least $10,000. You can't hold more than 25% of your total TSP balance there, so you need at least $40,000 in the TSP to start. There's also a $37 annual administrative fee on top of each fund's own expenses and any transaction fees. For most savers, the core funds already provide broad diversification at a fraction of the cost. The window mainly makes sense for specific needs, such as a particular sector or a socially screened fund.

The bottom line

The TSP gives you everything you need for a diversified, very low-cost portfolio: a guaranteed fund, a bond index fund, U.S. large-cap and small/mid-cap stock index funds, and an international stock index fund. You can also choose one L Fund that combines all five for you. Your key decision isn't which fund will win next year. It's how much of your account belongs in stocks versus the G and F Funds, given your timeline, your pension and how you handle market drops.

Next, see how much you can put in this year in our 2026 TSP contribution limits guide, or learn how money comes out in TSP withdrawal rules.

Frequently asked questions

Keep learning

Want to keep tabs on your C, S, I, F and G Fund mix all year? See what's included in a TSP Maxing membership.