Fundamentally, STFFX.US, a Schwab Target Retirement fund, is priced based on its net asset value (NAV). This NAV fluctuates due to the underlying assets held within the fund. Stock Market Performance: The fund invests heavily in stocks. Rising stock prices generally increase the fund's NAV and therefore its price.

Bond Market Fluctuations: Bond prices and yields have an inverse relationship. Increased bond yields generally drive down bond prices, negatively impacting the fund's NAV.

Target Date Proximity: As the target date nears, the fund's asset allocation shifts towards more conservative investments, like bonds. This gradual de-risking affects its growth potential and price.

Expense Ratio: While not directly affecting the day-to-day price, the expense ratio reduces the fund's overall returns, subtly impacting its long-term price performance.

Fund Flows: Significant inflows of cash into the fund can necessitate buying more assets, potentially driving up prices of holdings. Conversely, large outflows may require selling assets, possibly lowering prices.