Expense ratios and tracking error are two critical metrics that can significantly impact your investment returns over time. Expense ratios represent the annual fees charged by the fund to cover operating costs, typically ranging from 0.03% to 1% or higher. For example, an expense ratio of 0.1% means you'll pay $10 annually for every $10,000 invested. The best index funds typically maintain expense ratios below 0.1%, helping maximize your long-term returns. Over a 30-year investment horizon, even a small difference in expense ratios can result in thousands of dollars in saved costs. To put this in perspective, a $100,000 investment with a 0.03% expense ratio versus a 0.3% ratio could save you over $30,000 in fees over 30 years, assuming average market returns.