TSP funds are the investment options inside the Thrift Savings Plan, and they come in three tiers: five low-cost individual index funds labeled G, F, C, S, and I; eleven Lifecycle (L) Funds that blend those five automatically based on a target retirement year; and a mutual fund window that opens access to thousands of outside mutual funds for participants who meet the balance requirements. Most federal employees and service members will find everything they need in the first two tiers.
The Five Individual Funds
Federal law directs the Federal Retirement Thrift Investment Board to offer five core funds, each tracking a different slice of the market.1Office of the Law Revision Counsel. 5 USC 8438 – Investment of Thrift Savings Fund Expense ratios sit around 0.034% per year, roughly 34 cents per $1,000 invested.2The Thrift Savings Plan (TSP). Expenses and Fees
G Fund
The G Fund holds special-issue Treasury securities created exclusively for the TSP. Its interest rate equals the weighted average yield of all outstanding marketable Treasury securities with four or more years until maturity.1Office of the Law Revision Counsel. 5 USC 8438 – Investment of Thrift Savings Fund Principal never drops. That safety is why the G Fund is the default investment for new accounts, and why its long-run returns typically trail the stock funds.
F Fund
The F Fund tracks the Bloomberg U.S. Aggregate Bond Index, a broad measure of investment-grade U.S. bonds covering government, corporate, and mortgage-backed debt.3The Thrift Savings Plan (TSP). F Fund Unlike the G Fund, F Fund values move with interest rates and credit conditions. When rates rise, bond prices fall, and the fund can post negative returns for a stretch. Over time it tends to earn slightly more than the G Fund in exchange for that volatility.
C Fund
The C Fund tracks the S&P 500 Index, holding stocks from roughly 500 of the largest U.S. companies. Those companies represent about 80% of the total American stock market by value.4The Thrift Savings Plan (TSP). C Fund It’s the workhorse equity holding for most participants: high growth potential across decades, with real swings in any single year.
S Fund
The S Fund tracks the Dow Jones U.S. Completion Total Stock Market Index, which covers every U.S. publicly traded stock not already in the S&P 500.5The Thrift Savings Plan (TSP). S Fund That means small and mid-sized companies. Holding both the C Fund and the S Fund gives you exposure to essentially the entire U.S. stock market.
I Fund
The I Fund tracks the MSCI EAFE Index, which covers large and mid-sized companies across developed markets in Europe, Australasia, and the Far East, spanning more than twenty countries outside the United States.6The Thrift Savings Plan (TSP). Federal Retirement Thrift Investment Board Approves New Benchmark Index for the I Fund Foreign markets don’t always move in step with American ones, so the I Fund adds geographic diversification. Currency movements between the dollar and foreign currencies also affect returns.
Lifecycle Funds
Lifecycle Funds bundle the five individual funds into a single target-date portfolio. You pick the L Fund whose target year is closest to when you expect to start withdrawing, and the fund handles the mix. The TSP currently offers eleven of them: L Income, L 2030, L 2035, L 2040, L 2045, L 2050, L 2055, L 2060, L 2065, L 2070, and L 2075.7The Thrift Savings Plan (TSP). Lifecycle Funds
Each L Fund follows a glide path, gradually shifting from stock-heavy allocations toward bonds and government securities as the target date nears. That shift happens automatically every quarter, so a participant who chose L 2050 in their twenties holds a much more aggressive stock-and-bond mix than someone nearing retirement in L 2030.7The Thrift Savings Plan (TSP). Lifecycle Funds Between quarterly adjustments, the fund rebalances daily to keep the allocation on track.8The Thrift Savings Plan (TSP). L 2030
Once a fund reaches its target date, it rolls into the L Income Fund, which is designed for people already drawing down their accounts. L Income leans heavily on the G Fund and F Fund, aiming to preserve capital while generating modest returns. If you don’t want to think about asset allocation, an L Fund is the simplest path.
The Mutual Fund Window
The mutual fund window lets participants invest in thousands of outside mutual funds beyond the core lineup. It exists for people who want exposure to specific sectors, asset classes, or strategies the five individual funds don’t cover. Flexibility comes with higher costs and stricter rules.
To open the window, you need at least $40,000 in your TSP account, and your first transfer into the window must be at least $10,000. At no point can more than 25% of your total TSP balance sit inside the window.9The Thrift Savings Plan (TSP). Mutual Fund Window
Three fees apply on top of whatever expense ratio the outside mutual fund itself charges:
- A $37 annual administrative fee, so window users don’t shift costs to other participants.
- A $95 annual maintenance fee, charged by the brokerage service provider.
- A $28.75 per-trade fee, assessed every time you buy or sell a fund inside the window.9The Thrift Savings Plan (TSP). Mutual Fund Window
For most participants, the five core funds already provide broad market coverage at a fraction of the cost. The window makes sense mainly for experienced investors working from a specific strategy.
Moving Money Between Funds
You can move money among the individual funds and lifecycle funds through interfund transfers. Each calendar month, your first two transfers can redistribute money among any of the TSP funds. After those two, additional transfers for the rest of the month can only move money into the G Fund.10The Thrift Savings Plan (TSP). How to Change Your TSP Investments The restriction is designed to discourage frequent trading. For any reasonable rebalancing plan, two free moves per month is enough.
Why the Fees Matter
The TSP’s expense ratios are among the lowest of any retirement plan in the country. In 2025, the net administrative expense ratio for the core funds ranged from 0.033% to 0.034%, meaning a participant with a $100,000 balance paid roughly $34 in annual fees across all five individual funds.2The Thrift Savings Plan (TSP). Expenses and Fees The average expense ratio for a comparable private-sector index fund runs several times higher. Compounded across a 30-year career, that gap turns into real money.
The Federal Retirement Thrift Investment Board hires private-sector investment managers to run each fund and replicate its benchmark index. The Board’s overriding legal duty is to act solely in the interest of participants and beneficiaries, a fiduciary standard similar to what governs private pension plans.11Office of the Law Revision Counsel. 5 USC 8472 – Federal Retirement Thrift Investment Board
Traditional and Roth Are Separate From Fund Choice
One point of confusion worth clearing up: choosing between Traditional and Roth is a decision about when you pay tax on your contributions, not a decision about which fund holds the money. Traditional contributions go in before tax and are taxed at withdrawal; Roth contributions are taxed upfront and qualified withdrawals come out tax-free.12The Thrift Savings Plan (TSP). Traditional and Roth TSP Contributions Either type of contribution can be invested in any TSP fund. You pick the tax treatment separately from the investment.