Eric,
To get your monthly gains there are different approaches. I tend to just go to the tsp.gov site and check the balance for different dates. That, however, includes contributions so it might not be the best answer for what you want. I like this website, tsptalk.com, because you can track your actual % gain on the Auto Tracker. Its a great program, and measuring yourself against others provides a lot of feedback and perspective about just how well you can do in the TSP.
My philosophy, although I'm still not living by it yet, is that it is possible to get really incredible yearly returns by just making 4-8 moves per year. TSPTalk is about learning the signals and seeing the signs of market turns. Nobody ever gets them all the way right, but that's the goal. There are many here that provide very good technical analysis that will help you see the turning points. But beware, the market always seeks to exert maximum frustration. In this era of QE the rules have been quite distorted. I think the worst rule that we are subject to is the 4 hr time lag when we make an IFT. I've had small monthly gains turn into a monthly loss in those 4 hrs and with no more IFTs left till the next month to make the $ back.
The G and F funds are supposed to be the funds of safety, but a short visit to the F fund can be quite a disappointment, like this month. For me, I am going to only get in the F fund if I plan on being out of the stock funds for more than a month. Some of the same Technical Analysis rules that apply to the stock funds can also apply to the F fund though, so after being beat down for awhile it would have more of a potential upside.
The I fund is also very risky. In May of 2010 I lost 10% in the I fund in 3 days! I never recovered and was down 22-23% at one point, and ended the year way negative. You are at the mercy of many foreign economies, plus the changing value of the dollar. That being said, sometimes the gains in the I fund are fantastic. I do take the bait sometimes.
