The Best Index Funds for Long-Term Investors

Index funds have earned their reputation as the workhorse of long-term wealth building. Decades of evidence — academic research, SPIVA scorecards, and the track records of millions of ordinary investors — confirm that a simple portfolio of low-cost index funds outperforms most actively managed alternatives over long periods. The challenge is not making the case for index funds; it is choosing the right ones from among hundreds of options.

This guide focuses on the best index funds specifically for long-term investors: those with a 10-year-plus horizon building toward retirement or financial independence. The evaluation criteria are expense ratio (the primary determinant of long-term performance differences), index quality, fund size and liquidity, and suitability as a core portfolio holding.

Table of Contents

1. What Makes an Index Fund Great for Long-Term Investors
2. Best U.S. Total Market Index Funds
3. Best S&P 500 Index Funds
4. Best International Index Funds
5. Best Bond Index Funds
6. Specialty and Factor Index Funds
7. How to Build a Complete Portfolio

What Makes an Index Fund Great for Long-Term Investors

Not all index funds are equally suited for long-term investors. The criteria that matter most over 20-30 year holding periods:

Expense ratio: The most important variable. A 0.50% expense ratio versus a 0.03% ratio on the same underlying index generates a difference of roughly 25% in final portfolio value over 30 years, assuming identical pre-fee returns. For long-term investors, there is no justification for choosing a higher-cost fund tracking the same index as a lower-cost competitor.

Breadth of index: Broader indexes provide more diversification. A total market fund holding 3,500+ stocks eliminates company-specific and sector-specific risks that narrower indexes (S&P 500, which holds 500 stocks) carry to a modest degree. For a truly long-term, hands-off investor, broader is generally better.

Tracking error: How closely does the fund follow its benchmark? Tracking error beyond the expense ratio indicates operational inefficiencies. The best index funds have near-zero tracking error relative to their stated benchmark.

Fund size and liquidity: Large funds have tighter bid-ask spreads (for ETFs), more liquidity for large transactions, and are essentially immune to closure risk. Avoid funds with under $1 billion in assets for core long-term holdings.

Tax efficiency: In taxable accounts, index funds are inherently more tax-efficient than actively managed funds due to lower turnover. ETF structures add an additional tax efficiency layer through the in-kind redemption mechanism that avoids distributing capital gains to shareholders.

Best U.S. Total Market Index Funds

Total market funds provide the broadest possible U.S. equity diversification — covering large, mid, small, and micro-cap stocks across all sectors. For a long-term buy-and-hold investor who wants to own the entire U.S. market in one fund, these are the gold standard.

Vanguard Total Stock Market ETF (VTI) — Expense Ratio: 0.03%

VTI tracks the CRSP US Total Market Index, holding approximately 3,600–3,900 U.S. stocks weighted by market capitalization. It is the largest index ETF in the world by assets and one of the most widely held long-term investments by individual investors. Its 0.03% expense ratio means you pay $0.30 per year for every $1,000 invested. VTI's size ($400+ billion in assets) guarantees negligible bid-ask spreads, extensive liquidity, and effectively zero closure risk. For most long-term investors, VTI is the single best one-fund U.S. equity holding available.

The equivalent mutual fund is VTSAX (Vanguard Total Stock Market Index Fund Admiral Shares) at 0.04%, requiring a $3,000 minimum. For investors using Vanguard accounts who prefer mutual funds over ETFs, VTSAX is functionally identical to VTI.

Fidelity ZERO Total Market Index Fund (FZROX) — Expense Ratio: 0.00%

FZROX charges literally nothing — 0.00% — and tracks a Fidelity proprietary index covering the entire investable U.S. stock market. Available only to Fidelity customers and not transferable to other brokerages, but for Fidelity account holders the zero expense ratio is a genuine advantage. Over 30 years, the 0.03% cost difference versus VTI adds up to several thousand dollars on a large portfolio — not enormous, but real. FZROX is best for investors who plan to hold at Fidelity long-term and do not anticipate transferring assets to another brokerage.

iShares Core S&P Total U.S. Stock Market ETF (ITOT) — Expense Ratio: 0.03%

ITOT tracks the S&P Total Market Index and holds over 2,000 U.S. stocks. It is functionally similar to VTI but from BlackRock's iShares family, making it a good alternative for investors using platforms where iShares ETFs trade without commissions. Performance and holdings are nearly identical to VTI over any extended period.

Best S&P 500 Index Funds

S&P 500 funds cover approximately 80% of total U.S. market capitalization, focused on the 500 largest companies. Long-term performance versus total market funds is very similar since large-caps dominate both by weight. S&P 500 funds are the most widely held index funds in the world and carry the longest track records.

Vanguard S&P 500 ETF (VOO) — Expense Ratio: 0.03%

VOO is the world's second-largest ETF and one of the most owned investments globally. It tracks the S&P 500 with near-zero tracking error at 0.03% annually. For any long-term investor seeking U.S. large-cap exposure, VOO is the benchmark. The S&P 500 has returned approximately 10% annually over the past century — VOO captures essentially 100% of that return after its minimal fee. Buffett has repeatedly stated that an S&P 500 index fund is his recommended investment for most people, and VOO is the most cost-effective way to implement that recommendation.

iShares Core S&P 500 ETF (IVV) — Expense Ratio: 0.03%

IVV is functionally identical to VOO — same index, same expense ratio, similar tracking error. Managed by BlackRock, it is one of the most liquid ETFs in existence. The primary practical difference from VOO is slight variation in dividend distribution timing and the fact that it is available without restrictions at more brokerages. Either VOO or IVV serves equally well as an S&P 500 core holding.

Fidelity 500 Index Fund (FXAIX) — Expense Ratio: 0.015%

FXAIX is a mutual fund (not an ETF) tracking the S&P 500 at just 0.015% — even cheaper than VOO on a fee basis and available with no minimum investment at Fidelity. For Fidelity account holders who prefer mutual funds, FXAIX provides the cheapest S&P 500 exposure available. It cannot be transferred to another brokerage without selling, but for buy-and-hold Fidelity investors it has a genuine cost advantage.

Best International Index Funds

International diversification reduces the risk that U.S.-specific events — political, regulatory, or economic — dominate your portfolio outcomes. The U.S. represents about 60% of global market capitalization; an international allocation gives you exposure to the remaining 40%.

Vanguard Total International Stock ETF (VXUS) — Expense Ratio: 0.07%

VXUS is the most comprehensive international equity fund available, holding approximately 8,000 stocks from developed and emerging markets in Europe, the Asia-Pacific region, Canada, and developing economies. It covers virtually every publicly traded stock outside the United States in a single fund. VXUS paired with VTI gives you a complete global equity portfolio covering essentially every publicly traded company in the world. For most long-term investors who want international exposure without complexity, VXUS is the single best choice.

Vanguard Developed Markets Index Fund (VEA) — Expense Ratio: 0.05%

VEA covers developed international markets only — Europe, Japan, Canada, Australia, and others — excluding emerging markets. Slightly cheaper than VXUS and lower volatility (developed markets are more stable than emerging). For investors who want international exposure but prefer to avoid the additional volatility of Chinese, Indian, Brazilian, and other emerging market stocks, VEA provides broad developed-market diversification at a slightly lower cost.

iShares Core MSCI Total International Stock ETF (IXUS) — Expense Ratio: 0.07%

IXUS is iShares' equivalent to VXUS, tracking a slightly different international index (MSCI All Country World ex-USA IMI vs. FTSE Global All Cap ex-US for VXUS). Performance over long periods is effectively indistinguishable from VXUS. Available commission-free at more brokerages than VXUS, making it the preferred international holding for investors using TD Ameritrade, Schwab, or Robinhood.

Best Bond Index Funds

Bond index funds provide the portfolio-stabilizing function in a long-term portfolio — reducing volatility, providing income, and offering capital appreciation when stocks decline. For long-term investors, the primary bond consideration is choosing the right type of bond exposure for their allocation.

Vanguard Total Bond Market ETF (BND) — Expense Ratio: 0.03%

BND is the definitive U.S. investment-grade bond index fund, holding over 10,000 bonds spanning government, corporate, and mortgage-backed securities across the full maturity spectrum (short, intermediate, and long-term). It provides comprehensive exposure to the entire U.S. investment-grade bond market in a single, low-cost fund. For most long-term investors adding bonds to a stock portfolio for stabilization, BND is the straightforward, comprehensive choice.

iShares Core U.S. Aggregate Bond ETF (AGG) — Expense Ratio: 0.03%

AGG tracks the Bloomberg U.S. Aggregate Bond Index — the most widely followed benchmark for U.S. investment-grade bonds. Functionally nearly identical to BND, though they track slightly different implementations of similar indexes. Both are acceptable core bond holdings; choose based on which is commission-free at your brokerage.

Vanguard Short-Term Bond ETF (BSV) — Expense Ratio: 0.04%

For investors approaching retirement or with shorter time horizons, BSV provides exposure to short-term (1–5 year maturity) government and investment-grade corporate bonds. Short-term bonds are much less sensitive to interest rate changes than long-term bonds, making BSV more stable in rising rate environments. The trade-off is lower yield than intermediate or long-term bond funds under most yield curve conditions.

Vanguard Inflation-Protected Securities Fund (VTIP) — Expense Ratio: 0.04%

VTIP holds Treasury Inflation-Protected Securities (TIPS), whose principal and interest payments adjust with the Consumer Price Index. For long-term investors concerned about inflation eroding fixed-income returns — a meaningful risk over 20-30 year horizons — allocating a portion of the bond holding to VTIP provides genuine purchasing power protection unavailable from nominal bonds.

Specialty and Factor Index Funds

Beyond core market-cap weighted indexes, several factor-based and specialty index funds have demonstrated long-term performance premiums supported by academic research. These are suitable as smaller satellite allocations within a core index fund portfolio, not replacements for it.

Avantis U.S. Small Cap Value ETF (AVUV) — Expense Ratio: 0.25%

AVUV targets small-cap value stocks — the combination of factors with the strongest historical return premium in academic research (the Fama-French three-factor model). It uses a rules-based approach to overweight profitable small-cap companies trading at low valuations. The higher expense ratio (0.25% versus 0.03% for core funds) is justified by the factor-based selection process. Suitable for investors who want a small-cap value tilt in addition to a core total market holding, typically as 10–20% of total equity allocation.

Vanguard Dividend Appreciation ETF (VIG) — Expense Ratio: 0.06%

VIG tracks an index of U.S. companies that have increased their dividends for at least 10 consecutive years, weighted by market cap. This quality screen produces a portfolio of financially strong, mature companies with growing income streams. VIG has demonstrated competitive total returns versus the S&P 500 with lower volatility — particularly valuable for investors approaching retirement who want equity growth with some income stability. Not primarily an income fund — the current yield is modest (around 1.8%) — but a quality-tilted alternative to a pure market-cap index.

Vanguard Real Estate ETF (VNQ) — Expense Ratio: 0.12%

VNQ provides exposure to U.S. REITs — real estate companies that own apartments, offices, warehouses, data centers, healthcare facilities, and more. REITs have historically provided returns competitive with equities over long periods, along with income that grows over time, and low correlation to the broader stock market. VNQ held in a Roth IRA (where its higher-than-average dividend yield is sheltered from taxation) is a popular long-term allocation for investors seeking real estate income exposure without property management.

How to Build a Complete Portfolio

The best index fund portfolio for a long-term investor is simple, low-cost, globally diversified, and matched to an appropriate stock-to-bond allocation for their age and risk tolerance. Here are three practical portfolio constructions using the funds reviewed above:

One-Fund Portfolio (Maximum Simplicity): 100% VTI or VXUS-weighted global fund. Appropriate for investors in their 20s–30s who want maximum growth with minimum complexity. Add a global equity fund like Vanguard Total World Stock ETF (VT) at 0.07% for true one-fund global coverage including both U.S. and international.

Two-Fund Portfolio (Global Equity): 60–70% VTI + 30–40% VXUS. Covers the entire global equity market at low cost. For a 30-year-old, this all-equity allocation maximizes long-term growth potential. Rebalance annually to maintain the target allocation.

Three-Fund Portfolio (Classic): 60% VTI + 20% VXUS + 20% BND. The three-fund portfolio — the foundational approach recommended by Bogleheads and many fee-only financial advisors — covers the entire global stock and bond market. Adjust the stock/bond split by age (more stocks when young, more bonds as retirement approaches). This three-fund combination at average expense ratios of roughly 0.04% is genuinely difficult to improve upon for most investors.

Four-Fund Portfolio (With Real Estate): 55% VTI + 15% VXUS + 20% BND + 10% VNQ. Adds real estate diversification through REITs, providing additional income and a real asset component. Best held with the REIT allocation in a tax-advantaged account due to REIT dividend taxation as ordinary income.

The specific percentage allocations matter less than the underlying commitment: stay invested through market volatility, maintain a diversified allocation appropriate for your time horizon, keep costs minimal, and contribute consistently over decades. The index funds above — VTI, VOO, VXUS, BND — form the foundation of more wealth-building portfolios in America than virtually any other combination of investments, and for good reason.