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TSP Funds Explained: G, F, C, S, and I

Updated June 2026 · ~6 min read

The Thrift Savings Plan keeps things refreshingly simple: instead of hundreds of confusing options, you get five core index funds, each a single letter. Here's what G, F, C, S, and I actually hold, how risky each is, and how to think about combining them.

The five core funds at a glance

Fund	What it holds	Risk
G	Special U.S. Treasury securities issued just for the TSP	Lowest — can't lose value
F	U.S. investment-grade bonds (a broad bond index)	Low to moderate
C	Large U.S. company stocks (S&P 500)	Higher
S	Small and mid-size U.S. company stocks	Highest of the U.S. stock funds
I	International stocks (developed and emerging markets outside the U.S.)	Higher, plus currency swings

The G Fund — the safe harbor

The G Fund invests in government securities issued specially for the TSP. Its key feature: the share price never goes down. You won't get rich on it — returns are modest — but you also can't lose your principal. It's where many people park money they can't afford to risk, or shift toward as they near retirement.

The F Fund — bonds

The F Fund tracks a broad U.S. investment-grade bond index. It usually earns a bit more than the G Fund over time, but unlike the G Fund its price can fall — especially when interest rates rise. It adds diversification because bonds often (though not always) behave differently from stocks.

The C, S, and I Funds — the growth engines

These are the stock funds, where most long-term growth comes from — along with most of the short-term ups and downs.

C Fund: the 500 largest U.S. companies (the S&P 500). The classic "U.S. stock market" exposure.
S Fund: the rest of the U.S. market — small and mid-cap companies not in the S&P 500. Historically a bit more volatile than the C Fund, with strong long-run growth.
I Fund: stocks of companies outside the United States, across developed and emerging markets. Adds global diversification, but also exposes you to currency movements.

How to think about mixing them

There's no single "right" allocation, but a few principles hold for most people:

Time horizon drives risk. The further you are from needing the money, the more you can lean toward stock funds (C/S/I), which have historically out-earned G and F over long periods.
Closer to retirement, more stability. As your timeline shortens, shifting some money toward G and F reduces the chance a downturn hits right when you need to withdraw.
Diversify rather than chase. Picking last year's best fund rarely works. Spreading across funds smooths the ride.
Don't forget inflation. Playing it too safe for decades can mean your money doesn't grow enough to keep up with rising costs.

If choosing and rebalancing a mix sounds like work, the TSP's Lifecycle (L) Funds do it for you automatically.

Model different return assumptions in the calculator →

This article is for general education only and is not financial advice. CalculateTSP is independent and not affiliated with, endorsed by, or sponsored by the U.S. Department of Defense, DFAS, or the Federal Retirement Thrift Investment Board. Fund details can change; confirm current information at tsp.gov.