Investing in index funds is a cornerstone of modern portfolio theory, offering broad market exposure, diversification, and low costs. Among the various factors influencing the performance of an index fund, the expense ratio stands out as a critical determinant. A lower expense ratio means more of your money is working for you, compounding over time.
In this comprehensive guide, we'll explore some of the index funds with the lowest expense ratios available as of September 2025, compare their features, and discuss how to choose the right one for your investment goals.
Comparison of Top Low-Cost Index Funds
| Fund Name | Type | Expense Ratio | Minimum Investment | Asset Class | Notable Features |
|---|---|---|---|---|---|
| Fidelity 500 Index Fund (FXAIX) | Mutual Fund | 0.015% | $0 | U.S. Large Cap (S&P 500) | No minimum investment; broad market exposure |
| Fidelity ZERO Large Cap Index (FNILX) | Mutual Fund | 0.000% | $0 | U.S. Large Cap | Tracks Fidelity U.S. Large Cap Index |
| Schwab S&P 500 Index Fund (SWPPX) | Mutual Fund | 0.020% | $0 | U.S. Large Cap (S&P 500) | No minimum investment; low cost |
| Vanguard 500 Index Admiral Shares (VFIAX) | Mutual Fund | 0.040% | $3,000 | U.S. Large Cap (S&P 500) | Requires minimum investment; reputable fund manager |
| iShares Core S&P 500 ETF (IVV) | ETF | 0.030% | $0 | U.S. Large Cap (S&P 500) | Highly liquid; low expense ratio |
| Vanguard S&P 500 ETF (VOO) | ETF | 0.030% | $0 | U.S. Large Cap (S&P 500) | Broad market exposure; low cost |
| SPDR S&P 500 ETF Trust (SPY) | ETF | 0.095% | $0 | U.S. Large Cap (S&P 500) | One of the oldest ETFs; high liquidity |
| Vanguard Total Stock Market ETF (VTI) | ETF | 0.030% | $0 | U.S. Total Market | Comprehensive market coverage |
| Schwab Total Stock Market Index Fund (SWTSX) | Mutual Fund | 0.030% | $0 | U.S. Total Market | Broad exposure; low cost |
| Fidelity Total Market Index Fund (FSKAX) | Mutual Fund | 0.015% | $0 | U.S. Total Market | No minimum investment; low expense ratio |
Understanding Expense Ratios
The expense ratio represents the annual fee expressed as a percentage of average assets under management. For instance, an expense ratio of 0.015% means that for every $1,000 invested, $0.15 is used to cover the fund's operating expenses. Lower expense ratios are advantageous because they reduce the drag on investment returns over time.
Why Expense Ratios Matter
Compounding Effect: Lower fees allow more of your investment to grow over time.
Long-Term Impact: Even small differences in expense ratios can lead to significant differences in returns over decades.
Cost Efficiency: Especially important for passive investments like index funds, where the goal is to mirror market performance rather than outperform it.
Performance Comparison
While expense ratios are crucial, it's also important to consider the historical performance of these funds. Below is a comparison of the 5-year annualized returns for some of the funds listed above:
| Fund Name | 5-Year Annualized Return |
|---|---|
| Fidelity 500 Index Fund (FXAIX) | 14.6% |
| Fidelity ZERO Large Cap Index (FNILX) | 14.6% |
| Schwab S&P 500 Index Fund (SWPPX) | 14.8% |
| Vanguard 500 Index Admiral Shares (VFIAX) | 14.8% |
| iShares Core S&P 500 ETF (IVV) | 14.8% |
| Vanguard S&P 500 ETF (VOO) | 14.8% |
| SPDR S&P 500 ETF Trust (SPY) | 14.7% |
| Vanguard Total Stock Market ETF (VTI) | 10.1% |
| Schwab Total Stock Market Index Fund (SWTSX) | 10.1% |
| Fidelity Total Market Index Fund (FSKAX) | 10.1% |
Note: Past performance is not indicative of future results.
Choosing the Right Index Fund for You
When selecting an index fund, consider the following factors:
1. Investment Vehicle: Mutual Fund vs. ETF
Mutual Funds: Purchased at the end of the trading day; may have minimum investment requirements.
ETFs: Traded throughout the day like stocks; no minimum investment; may incur brokerage fees.
2. Expense Ratio
Opt for funds with lower expense ratios to minimize costs. For instance, Fidelity's FXAIX and FNILX offer some of the lowest expense ratios in the industry.
3. Fund Size and Liquidity
Larger funds tend to have better liquidity, making it easier to buy and sell shares without significantly affecting the price.
4. Tracking Error
This measures how closely the fund's performance matches that of its benchmark index. A lower tracking error indicates better performance alignment.
5. Fund Manager Reputation
Consider the reputation and reliability of the fund manager. Established firms like Vanguard, Fidelity, and Schwab have long-standing histories of managing index funds effectively.
Top Picks Summary
Based on the factors above, here are some top picks:
Best Overall Mutual Fund: Fidelity 500 Index Fund (FXAIX) – Offers a low expense ratio of 0.015% and strong historical performance.
Best Overall ETF: iShares Core S&P 500 ETF (IVV) – Provides low costs and high liquidity.
Best Total Market Exposure: Vanguard Total Stock Market ETF (VTI) – Covers the entire U.S. stock market with a low expense ratio of 0.030%.
Final Thoughts
Selecting an index fund with a low expense ratio is a smart strategy for cost-conscious investors aiming for long-term growth. While expense ratios are a significant factor, it's essential to consider other aspects like fund size, liquidity, and tracking error. By carefully evaluating these factors, you can choose an index fund that aligns with your investment goals and financial situation.
Remember, the key to successful investing is consistency and patience. By investing in low-cost index funds and allowing your investments to grow over time, you can build a solid foundation for your financial future.
Note: The information provided in this guide is based on data available as of September 2025. Always conduct your own research or consult with a financial advisor before making investment decisions.
Sources
Fidelity 500 Index Fund (FXAIX) – Fidelity Investments: https://fundresearch.fidelity.com/mutual-funds/summary/315911750
Fidelity ZERO Large Cap Index Fund (FNILX) – Fidelity Investments: https://fundresearch.fidelity.com/mutual-funds/summary/315911628
Schwab S&P 500 Index Fund (SWPPX) – Schwab Asset Management: https://www.schwabassetmanagement.com/products/swppx
Vanguard 500 Index Fund Admiral Shares (VFIAX) – Vanguard: https://investor.vanguard.com/investment-products/mutual-funds/profile/vfiax
iShares Core S&P 500 ETF (IVV) – iShares: https://www.ishares.com/us/products/239726/ishares-core-sp-500-etf
Vanguard S&P 500 ETF (VOO) – Vanguard: https://investor.vanguard.com/investment-products/etfs/profile/voo
SPDR S&P 500 ETF Trust (SPY) – State Street Global Advisors: https://www.ssga.com/us/en/intermediary/etfs/spdr-sp-500-etf-trust-spy
Vanguard Total Stock Market ETF (VTI) – Vanguard: https://investor.vanguard.com/investment-products/etfs/profile/vti
Schwab Total Stock Market Index Fund (SWTSX) – Schwab Asset Management: https://www.schwabassetmanagement.com/products/swtsx
Fidelity Total Market Index Fund (FSKAX) – Fidelity Investments: https://fundresearch.fidelity.com/mutual-funds/summary/315911750