Performance of Underlying Assets: AMACX.US primarily invests in other American Century mutual funds. Their performance directly influences AMACX's price. Strong returns in those underlying funds boost AMACX's value, while poor performance drags it down.

Market Conditions: Broad market trends and economic factors impact AMACX. A bullish market usually leads to higher returns, while a bearish market causes losses. Interest rates, inflation, and global events also play a role.

Fund Expenses: AMACX's expense ratio and operating costs detract from its returns. Higher expenses reduce the overall value of the fund, impacting its price negatively.

Investor Demand: The demand for AMACX shares affects its price. Increased demand typically drives the price upward, while selling pressure can cause the price to decrease.

Fund Manager Decisions: The fund manager's investment strategy and decisions regarding asset allocation have a substantial effect on AMACX's performance and, subsequently, its price.