This is no different from investing for your retirement on your own by buying index funds. Where you should put your money depends upon your tolerance for risk, and how long it will be before you retire.
The G Fund, which consists entirely of government-backed securities, is absolutely safe. The value can never go down. On the other hand, it’s like putting all your money into savings bonds. The returns it produces are very small. So, money you put in there is safe, but it’s not going to grow very fast. Over the last 12 months, the G fund has returned just over 4%. If all your money is in the G Fund, you’re going to be fairly poor in retirement.
The C Fund is more like a large-cap stock index fund. It’s invested in the 500 largest stocks in the market. Unlike the G Fund, the value might go up, or it might go down. If you see the S&P average on the stock market go up, your C Fund holdings will be going up a similar percentage, and vice-versa. So, there’s more risk, but there’s the possibility of higher returns. Over the last 12 months, the C Fund has returned over 34%.
The S and I Funds invest in broad groups of small-cap stocks and international stocks, respectively. Like the C Fund, they might go up, or they might go down, depending upon how the markets are doing. They tend to be more volatile than the large-cap stocks, going up and down more quickly. So, there’s more risk, but the possibility of greater rewards. Over the last 12 months, the S and I Funds have returned over 51% and 45%, respectively.
The F Fund invests in a broad collection of bonds. These aren’t as safe as government-backed securities (the G Fund), but are generally less volatile than the stock funds (C, S, and I). Over the last 12 months, the F Fund has returned just under 5%.
If you’re getting close to retirement, you don’t want to have much risk, because you’re going to need to start drawing that money fairly soon. So, if the markets take a dive, you won’t be able to wait it out. But if you’re still more than, say, 10 years away from retirement, you should be heavily invested in stocks. Historically, in the long run, they have always out-performed safer investments, like government securities or bonds.
If you’re in your 20s, I’d tell you to put 35% in C, 25% in S, 25% in I, 10% in F, and 5% in G. If you’re in your 40s, maybe 40% in C, 20% in S, 20% in I, 10% in F, and 10% in G. In other words, the older you get, and the closer to retirement, the more you want to start shifting from the riskiest (but potentially best-performing) funds to the safer but duller ones.
The TSP website has a lot of this information, and your personnel office can surely give you some of the pamphlets the TSP folks turn out that explain the pros and cons of different TSP allocations.