All three stock-oriented TSP funds suffered losses in August, the steepest by the small company S fund, which fell 4.19 percent while the international stock I fund dropped 1.77 percent and the large company stock C fund (which tracks the S&P 500) fell 1.59. percent.

The bond F fund rose 2.6 percent, however, and the government securities G fund rose 0.18 percent. Bond buying pressure around the world has pushed yields down and bond prices up, which has been a drag on the G Fund due to lower rates, but a boon for the F Fund. (See also, Interest Rate Cuts and the G Fund.)

The stock fund declines in turn produced losses in all of the lifecycle L funds: Income, -0.12; 2020, -0.24; 2030, -0.96; 2040, -1.22; 2050, -1.46.

August was an interesting month for the TSP, with increased volatility compared to the rest of the calendar year so far. But September has been a historically volatile month for the TSP as well, and the S&P 500 is currently stuck in a trading range that could break up or down.