The TSP offers five individual investment funds plus a suite of Lifecycle (L) Funds. Understanding the difference is essential before deciding where your contributions go — because the default fund (the G Fund) is not always the right choice for your career stage.

The G Fund: Government Securities

The G Fund invests exclusively in short-term U.S. Treasury securities specially issued to the TSP. It is the only fund in the TSP that is guaranteed not to lose money — the principal is always protected. However, because of this guarantee, its returns are generally lower than stock-based funds over long time horizons.

Per TSP.gov, the G Fund's interest rate is set monthly based on the weighted average yield of all U.S. Treasury securities with four or more years to maturity. In periods of rising interest rates, the G Fund rate adjusts relatively quickly. It is appropriate for members approaching retirement or those with very short time horizons who cannot tolerate any loss of principal.

The F Fund: Fixed Income

The F Fund tracks the Bloomberg U.S. Aggregate Bond Index — a broad index of U.S. bonds including government, corporate, and mortgage-backed securities. Unlike the G Fund, the F Fund can lose value when interest rates rise (bond prices and interest rates move inversely). It offers slightly higher potential returns than the G Fund with moderate risk. It is appropriate for conservative investors with medium to long time horizons.

The C Fund: Common Stock

The C Fund tracks the S&P 500 Index, which represents the 500 largest U.S. publicly traded companies. Historically, the C Fund has provided the highest long-term returns of any TSP individual fund, but it also experiences significant short-term volatility. Over any given year, the C Fund may fall substantially. Over a 20–30 year career, the C Fund has historically recovered from downturns and delivered strong cumulative growth. It is appropriate for members with long time horizons (10+ years to retirement) who can tolerate significant short-term fluctuation.

The S Fund: Small Cap Stock

The S Fund tracks the Dow Jones U.S. Completion Total Stock Market Index, which includes U.S. stocks not included in the S&P 500 — primarily small and mid-cap companies. Small-cap stocks historically offer higher potential long-term returns than large-cap stocks, with higher volatility. The S Fund is appropriate for members with long time horizons and a higher risk tolerance.

The I Fund: International Stock

The I Fund tracks the MSCI EAFE (Europe, Australasia, Far East) Index — international developed market stocks. It provides diversification outside the U.S. market. The I Fund carries additional risks including currency risk and geopolitical risk. It is appropriate as a diversification component for long-horizon investors, typically not as a primary fund.

The Lifecycle (L) Funds: An All-in-One Option

If choosing among the five individual funds feels overwhelming, the Lifecycle Funds are designed for simplicity. Each L Fund (L2025, L2030, L2035, L2040, L2045, L2050, L2055, L2060, L2065) automatically adjusts its allocation between the five individual funds as the target retirement date approaches — becoming more conservative as retirement nears. The L Funds are based on the TSP Lifecycle Investment Strategy described on tsp.gov.

The L Fund with a date closest to your expected retirement year is generally appropriate for most members as a starting point. As of 2025, L Funds that have already reached their target date (past L2025, for example) have rolled into the most conservative allocation.

General Guidance by Stage of Service

Early career (0–10 years of service): Most TSP experts, including the TSP itself in its educational materials, acknowledge that members with 20+ years until retirement have time to absorb market volatility. A higher allocation to the C Fund, S Fund, and I Fund historically produces stronger long-term outcomes, though past performance does not guarantee future results.

Mid-career (10–15 years of service): A mixed allocation across C, S, I, and F Funds with gradual rebalancing toward stability as retirement approaches.

Near retirement (5 years or fewer to separation): The G Fund and F Fund become more appropriate as capital preservation takes priority over growth.

KEY TAKEAWAYS:

  • G Fund is the only TSP fund guaranteed not to lose money, but offers lower long-term growth potential
  • C Fund tracks the S&P 500 — highest long-term return potential, highest short-term volatility
  • S Fund (small cap) and I Fund (international) add diversification; both carry more volatility than the C Fund
  • Lifecycle Funds automatically rebalance for your target retirement year — appropriate for members who prefer simplicity
  • Early-career members with 20+ years to retirement have historically benefited from heavier stock-fund allocations