Federal Funds Rate: The primary driver. SFPXX invests in short-term government securities. When the Fed raises the federal funds rate, yields on these securities increase, leading to higher SFPXX yields and potentially a slight increase in its share price.

Treasury Bill Yields: SFPXX invests heavily in Treasury bills. As Treasury bill yields rise or fall, SFPXX's yield and price will follow suit.

Repo Rates: Repurchase agreements (repos) are another component of SFPXX's holdings. Changes in repo rates directly impact the fund's overall yield and indirectly influence its price.

Demand for Safe Assets: During times of economic uncertainty or market volatility, demand for safe assets like government securities increases. This can push up the prices of these assets, potentially leading to a minor increase in SFPXX's price.

Fund Management Fees: While typically very small, management fees can slightly offset the fund's yield, indirectly affecting its perceived value.

Overall Market Liquidity: Reduced liquidity in the short-term debt market can lead to temporary price fluctuations in SFPXX, although this is less common.