You're asking about asset allocation, and you will get diddly-squat help and info from TSP. So you have to learn how the funds correspond to regular investment vehicles and then take it from there.
The TSP funds break down like this:
G fund = equivalent of cash (based on short-term Treasury securities) --think money market funds and so forthF fund = bond index fund; benchmark is Barclay Capital US Aggregate, formerly Lehman Bros. It includes corporate, government, mortgage-backed, and foreign bond fundsC fund = medium- to large-cap equity (stock) fund; benchmark is the S&P 500, the top 500 publicly-traded US companies, as measured by their capitalizationS fund = small- to medium-cap equity fund; benchmark is the Dow Jones US Completion Index, formerly the Wilshire 4500 (the 4500 stocks too small to be in the S&P 500)I fund = international developed-country equity fund; benchmark is the EAFE Index (Europe, Australasia, Far East)Once you see the breakdown, you can use asset allocation advice to help you decide your best plan. For instance, a common recommendation for balancing investments in stocks vs bonds is to subtract your age from 110 (100 in more conservative versions.) Tack a percentage point on to the resulting figure, and that should be the percentage of your allocation to stock (equity) funds. So if you're 40 now, 110 - 40 --> 70% in stocks, 60% for a more conservative approach. Put the rest in bonds, aka the F fund.
The question with TSP is how to break down that equities (stocks) portion among C, S, and I. You need to have exposure to all three, because often when one or two slump, the other(s) do better. I seem to weight the C (S&P 500) fund a bit more heavily, and I wind up dividing my equity allocation on a 3-2-2 basis, with the higher portion to C and an equal amount to S and I. That's just from research I've done and my own tolerance (and need) for risk. Other people will break it down differently. I would have more in the I fund, but my second job has an IRA, and I'm invested in foreign bonds there, so I'm getting foreign exposure elsewhere.
For younger people like you, there's not a lot of point in having much in the G fund if you also have a money market fund or CD's or something similar going on the outside. The benefit of TSP is that the bond and equity funds are dirt cheap, easily 1/10 the cost of most other funds, so it makes sense to concentrate on them, and save cash elsewhere.
The L funds mix all five funds and reallocate according to how close you are to retirement. For a while, I had half my funds in L and half in my own mix, and I beat the L fund, until I stopped paying attention and got caught in the market crash. (My bad!) The TSP L funds didn't do so well compared to other targeted retirement funds, but there's a lot to be said for file-and-forget. And in the long run, people who stick with the same investment strategy do better than those who change around whenever they read a new article. A lot depends on how hands-on you want to be.
Google "asset allocation" to start to get a feel for how a mix of investments can help you. Just convert their recommendations to the TSP funds, and you'll get a general picture of what you might want to do.
btw, this is all from someone who stayed home with the kids for a long, long time, and who is now in major catch-up mode. I wish that I'd been investing 10 or 15 years ago!
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