The S&P 500 vs total market ETF debate is one of the most common questions among index fund investors, and it deserves a clear, data-driven answer rather than a vague “both are fine.” The short answer: the performance difference between the two has been trivially small over almost every historical period, but the total market ETF offers broader diversification, while the S&P 500 fund offers greater familiarity and slightly more liquidity. This guide covers exactly how the two differ, what the long-term performance data actually shows, and which one deserves a place in your specific portfolio.
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What Each Fund Actually Holds
Before comparing performance, it is essential to understand what each fund actually contains — because the difference is more nuanced than “500 stocks versus more stocks.”
The S&P 500 is a market-cap-weighted index of the 500 largest US publicly traded companies selected by a committee at S&P Dow Jones Indices. As of 2026, these 500 companies represent approximately 80% of the total US stock market capitalisation. The largest holdings — Apple, Microsoft, Nvidia, Amazon, Alphabet, Meta, Berkshire Hathaway — collectively represent roughly 25–30% of the index. The S&P 500 is entirely large-cap, covering no mid-cap or small-cap companies.
The total US stock market index — tracked by funds like VTI and FSKAX — holds essentially every publicly traded US company: approximately 3,500 to 4,000 stocks depending on the specific index used. In addition to the 500 large-cap companies in the S&P 500, it includes roughly 400–500 mid-cap companies and 2,500–3,000 small-cap companies. However, because the index is market-cap weighted, the additional companies are tiny in weight terms. The top 500 stocks in the total market fund represent approximately 83–85% of its total weight — almost identical to the S&P 500’s composition.
Performance Comparison — What the Data Shows
Over the past 20 years, the performance difference between S&P 500 index funds and total market index funds has been remarkably small — within a fraction of a percent in most periods. This near-identical performance is precisely what the market-cap weighting mathematics predicts. Since both indices are dominated by the same large-cap companies, their returns are highly correlated.
In periods when small and mid-cap stocks outperform large caps — such as the early 2000s recovery from the dot-com bust, when small-caps significantly outperformed — the total market fund has a modest advantage. In periods when large-cap technology companies dominate returns — as in the 2010s through the early 2020s — the S&P 500 and total market fund perform nearly identically, with a slight edge sometimes going to the S&P 500 due to its purer large-cap concentration.
The long-term academic evidence on the “small-cap premium” — the historical tendency of smaller companies to outperform larger ones over very long periods — suggests the total market fund should have a theoretical long-term advantage. However, this premium has been inconsistent in recent decades and may be partially arbitraged away as more investors seek it.
S&P 500 (VOO): ~13.0% per year
US Total Market (VTI): ~12.8% per year
Difference: ~0.2% per year
20-Year Annualised Returns (approximate):
S&P 500: ~10.4% per year
US Total Market: ~10.3% per year
Difference: ~0.1% per year
Correlation between S&P 500 and Total Market daily returns: ~0.999
Side-by-Side Comparison
| Feature | S&P 500 (VOO/IVV) | Total Market (VTI/FSKAX) |
|---|---|---|
| Number of holdings | ~500 | ~3,500–4,000 |
| Market cap coverage | ~80% of US market | ~100% of US market |
| Company size exposure | Large-cap only | Large, mid, and small-cap |
| Expense ratio (Vanguard) | 0.03% (VOO) | 0.03% (VTI) |
| Daily trading volume | Very high (SPY/IVV/VOO) | High (VTI) |
| 10-year return (approx.) | ~13.0% annualised | ~12.8% annualised |
| Correlation to each other | ~0.999 (near-perfect) | |
| Index selection | Committee-based | Rules-based, full market |
| Small-cap exposure | None | ~7–9% of portfolio |
The Arguments for Each Fund
Why Choose the S&P 500
The S&P 500 is the most widely recognised benchmark in the world. It is the standard against which virtually every professional fund manager is measured. This ubiquity creates practical advantages: S&P 500 ETFs like SPY, IVV, and VOO have the highest trading volumes of any ETFs in the world, meaning bid-ask spreads are extraordinarily tight. For investors who value simplicity and the psychological comfort of tracking the benchmark that dominates financial media coverage, the S&P 500 fund is the intuitive choice.
The S&P 500’s committee-based selection also acts as a crude quality filter. To be included, companies must meet profitability requirements — they must have reported positive earnings in the most recent quarter and positive cumulative earnings over the most recent four quarters. This excludes speculative, unprofitable companies that a purely rules-based total market index would automatically include. Whether this quality filter adds or detracts from returns over time is debatable, but it does mean the S&P 500 holds a somewhat higher-quality company set.
Why Choose the Total Market Fund
The total market fund’s strongest argument is philosophical: true diversification means owning the entire market, not just the largest segment of it. By excluding mid and small-cap companies entirely, the S&P 500 leaves out companies that may generate the next generation of outperformance. Small-cap stocks have historically delivered higher returns over very long periods — what academics call the “small-cap premium” — though this premium has been elusive in recent decades.
The total market fund also avoids the arbitrary boundary problem of the S&P 500. A company ranked 501st is excluded entirely; a company ranked 500th is included at full weight. This creates small discontinuities in the index’s composition that the total market fund avoids by holding essentially everything. For investors who believe in efficient markets and want the most complete exposure possible to US economic growth, the total market fund is the more theoretically pure choice.
The Specific Funds — VOO vs VTI vs IVV vs FSKAX
Among the most popular options for each index type, there are a few nuances worth understanding before choosing.
For S&P 500 exposure, VOO (Vanguard S&P 500 ETF) and IVV (iShares Core S&P 500 ETF) both charge 0.03% and are essentially identical in their holdings and returns. VOO has a slight edge in trading volume at Vanguard-platform investors, while IVV is slightly more popular at Fidelity and Schwab. SPY (SPDR S&P 500 ETF Trust) is the original S&P 500 ETF and the most traded security in the world by volume, but its 0.0945% expense ratio is three times higher than VOO and IVV for the same exposure. Long-term investors should avoid SPY and use VOO or IVV instead.
For total market exposure, VTI (Vanguard Total Stock Market ETF) at 0.03% and FSKAX (Fidelity Total Market Index Fund) at 0.015% are the leading choices. FZROX (Fidelity ZERO Total Market Index Fund) charges literally 0.00% but uses a proprietary index rather than the CRSP US Total Market Index used by VTI. FZROX is only available at Fidelity and cannot be transferred in-kind to another brokerage — a minor but non-trivial portability limitation.
Which One Should You Actually Choose?
Given the near-identical historical performance, the most honest answer is: it does not matter very much. Either choice is excellent. However, if pressed for a recommendation, here is a clear framework. If you are investing at Fidelity and plan to stay there, FZROX (0.00% fee) or FSKAX (0.015%) are hard to beat on cost. If you are investing at Vanguard, VTI and VOO both at 0.03% are essentially tied — choose VTI if you value the theoretical small-cap diversification, VOO if you prefer the pure S&P 500 benchmark. If you are investing at Schwab or another platform, SCHB (Schwab US Broad Market ETF, 0.03%) and SCHX (Schwab US Large-Cap ETF, 0.03%) are excellent equivalents.
The most important decision is not S&P 500 versus total market — it is ensuring you are in a low-cost, broadly diversified index fund at all, rather than paying 0.66% or more for active management that is unlikely to justify its cost. Once you have made that decision, the choice between these two excellent options is genuinely secondary.
Frequently Asked Questions
Is VTI better than VOO for long-term investing?
Based on historical data, neither VTI nor VOO is clearly better than the other over most time periods. Their 20-year annualised returns have been within 0.1–0.2% of each other, and their day-to-day correlation is approximately 0.999. VTI offers broader diversification including mid and small-cap companies, which may provide a slight advantage if the small-cap premium re-emerges. VOO provides pure large-cap S&P 500 exposure, which has slightly outperformed in periods dominated by large-cap technology leadership. Both are outstanding choices at 0.03% expense ratios. If you already own one and are considering switching to the other, the tax cost of selling in a taxable account almost certainly exceeds any potential performance benefit.
Should I hold both an S&P 500 fund and a total market fund?
No — this creates unnecessary overlap. Because the S&P 500 constitutes approximately 83% of the total market fund by weight, holding both is essentially just overweighting large-cap US stocks. If you want the total market, hold VTI or FSKAX. If you want the S&P 500, hold VOO or IVV. Holding both provides no meaningful diversification benefit and only adds portfolio complexity without purpose.
What about the Nasdaq-100 — is that a better index to track?
The Nasdaq-100 (tracked by QQQ and QQQM) holds the 100 largest non-financial companies listed on the Nasdaq exchange, which means it is heavily concentrated in technology. It has significantly outperformed the S&P 500 over the past 15 years due to the dominance of Apple, Microsoft, Nvidia, Amazon, and Google. However, it is far less diversified than either the S&P 500 or total market fund, and its concentrated technology exposure means it falls much harder during tech selloffs and interest rate increases. It is a sector bet, not a market bet, and carries commensurately higher risk for individual investors than a broad market index.
Does the choice between S&P 500 and total market matter more in a Roth IRA or a taxable account?
The account type does not change which fund is theoretically better — the performance and diversification characteristics are the same regardless of account wrapper. However, in a taxable account, the zero-fee advantage of FZROX is slightly offset by its portability limitations, and the tax efficiency of ETF structures (VTI, VOO) becomes more relevant. In a Roth IRA, mutual fund equivalents like FSKAX and FXAIX offer automatic investment features and easier dollar-based purchasing that some investors find convenient. The performance difference between these options in any account type remains negligible compared to the importance of choosing low-cost index funds over active management.
This article is for informational purposes only and does not constitute financial advice. Investment involves risk, including the possible loss of principal. Past performance is not indicative of future results. Please consult a qualified financial advisor before making investment decisions.