Federal Funds Rate: The target rate set by the Federal Reserve for overnight lending between banks significantly impacts money market fund yields and therefore the fund's price.

Short-Term Interest Rates: Prevailing rates on short-term debt instruments (Treasury bills, commercial paper, certificates of deposit) directly influence the fund's returns.

Credit Risk: The creditworthiness of issuers whose securities are held in the fund impacts the perceived risk and thus affects the fund's price; higher risk leads to potentially lower price.

Maturity of Holdings: The average maturity of securities in the portfolio affects sensitivity to interest rate changes; longer maturities can lead to greater price fluctuations.

Supply and Demand: Overall demand for money market funds and the specific MMTHX.US fund can impact its share price, as increased demand may drive the price slightly higher.

Fund Expense Ratio: The fees charged by the fund manager can impact the net return to investors and therefore influences the price to some extent.