The S&P 500 index fund is the default first investment for most US retail investors. Three funds dominate: Vanguard VOO, iShares IVV, and SPDR SPY. They all track the same index. The differences are in expense ratios, structure, and trading liquidity. This article uses S&P Dow Jones Indices data, Morningstar fund analysis, and Bogleheads wiki guidance to compare them on the metrics that actually matter for buy-and-hold investors.
- 5-year total return for all three (closer than you’d expect)
- Expense ratio differences and 30-year compounding impact
- Tax efficiency — why SPY’s structure matters in taxable accounts
- The Bogleheads consensus pick
The 5-year return — within rounding error
S&P Dow Jones Indices data (2019-2024 period):
| Fund | 5-year total return | Expense ratio | Annual expense difference |
|---|---|---|---|
| VOO | 90.5% | 0.03% | baseline |
| IVV | 90.4% | 0.03% | -0.0% |
| SPY | 90.2% | 0.0945% | -0.06%/year |
For a $10,000 investment over 5 years: VOO and IVV both end at ~$19,050. SPY ends at ~$19,020. The $30 difference compounds modestly over 5 years and meaningfully over 30 years.
The 30-year compounding math
The expense ratio difference doesn’t matter much in 5 years. It compounds significantly over investing lifetimes.
💡 30-year illustration — $10,000 invested, 7% annual return assumption, 0% expenses → $76,123. With VOO (0.03% expense) → $75,479. With SPY (0.0945%) → $74,103. The SPY-vs-VOO gap over 30 years on this single contribution: $1,376 (1.8% of total).
Compounding the difference matters, but the gap is small. For the typical investor, the $1,376 over 30 years on $10,000 is real but not life-changing. The bigger lever remains contribution rate, not expense ratio choice between three funds within 0.07% of each other.
The structural difference — UIT vs ETF
A subtle but real difference:
- VOO — Open-end ETF. Can use in-kind redemptions, fully reinvest dividends, optimize for tax efficiency.
- IVV — Open-end ETF. Same structural advantages as VOO.
- SPY — Unit Investment Trust (UIT). Cannot reinvest dividends (must distribute as cash). Slightly less tax-efficient.
For buy-and-hold investors in taxable accounts, this structural difference favors VOO or IVV. In tax-advantaged accounts (IRA, 401(k)), the difference disappears.
When SPY is actually the right choice
SPY’s 3x daily trading volume of VOO is a real advantage for active traders:
Tightest bid-ask spread. Most options liquidity. Best for short holds.
Lowest expense. Best for IRAs, taxable long-term accounts.
Identical to VOO functionally. Choose by brokerage availability.
0% expense ratio. Mutual fund. Best in Fidelity-hosted accounts.
Tracking error — small but measurable
Tracking error measures how closely a fund follows its index. Lower is better.
| Fund | 5-year tracking error |
|---|---|
| VOO | 0.02% |
| IVV | 0.02% |
| SPY | 0.04% |
All three track extremely closely. SPY’s slightly higher tracking error reflects its UIT structure (less flexibility for fund managers). The difference is small enough to be statistically marginal but is real over decades.
The Bogleheads consensus
Bogleheads.org (the largest community of long-term index investors, ~150,000 members):
- VOO is the #1 recommendation for taxable accounts. Lowest expense + Vanguard’s investor-owned structure.
- FXAIX wins for Fidelity-hosted accounts with 0% expense ratio.
- IVV is the equal alternative to VOO if your brokerage doesn’t list VOO commission-free.
- SPY is for active traders only — buy-and-hold investors lose money to its higher expenses.
Most importantly: pick one and don’t switch. Switching between functionally identical funds creates taxable events with no offsetting benefit.
Beyond just the S&P 500
Bogleheads three-fund portfolio (the most-recommended starting allocation):
- VTI (Total US Stock Market) — 60% — broader than S&P 500, includes mid + small cap
- VXUS (Total International Stock) — 30% — international diversification
- BND (Total US Bond Market) — 10% — bond stabilizer
For pure S&P 500 simplicity, VOO + VXUS + BND is the simpler 3-fund version. Either approach is significantly better-diversified than S&P 500 alone for risk balance.
The bottom line
For 2025 retail investors:
- VOO is the default for taxable accounts. Lowest fees, best structure.
- FXAIX in Fidelity-hosted retirement accounts if you have access.
- SPY only if you actively trade — the higher expense ratio loses meaningful money over decades for buy-and-hold.
- IVV is acceptable as a near-perfect substitute for VOO.
- Don’t switch — the fund choice differences are smaller than the cost of switching.
Most importantly, the difference between VOO and SPY is dwarfed by the difference between investing $200/month vs $400/month. Optimize contribution rate before optimizing fund selection.
Investing books that align with the index-fund evidence
The S&P 500 index-fund case is built on decades of Bogle’s research. Three books synthesize that evidence into actionable portfolio frameworks — they’re the canon every serious index investor reads:
The Little Book of Common Sense Investing (John C. Bogle)
Price · $15-22 — Bogle's index-fund manifesto
+ Pros
- · Author founded Vanguard and invented the index fund — primary source
- · Updated 10th anniversary edition includes post-2008 data
- · Short, dense — read in a weekend, re-read annually
− Cons
- · Repetitive in places — Bogle reinforces key points across chapters
- · Some examples skew toward US-only investing (limited international coverage)
Price, availability, and ratings can change; verify details on the retailer page before buying.
The Bogleheads' Guide to Investing (Larimore, Lindauer, LeBoeuf)
Price · $18-25 — community-distilled wisdom
+ Pros
- · Comprehensive — covers IRAs, 401k, taxable accounts, and asset allocation
- · Written by Vanguard-community veterans, not Wall Street pros
- · Concrete action steps + portfolio templates
− Cons
- · Longer than Bogle's Little Book — denser reading
- · Tax-law specifics may need updating for current rules
Price, availability, and ratings can change; verify details on the retailer page before buying.
A Random Walk Down Wall Street (Burton Malkiel)
Price · $18-25 — academic foundation of efficient-markets case
+ Pros
- · 13th edition includes ETFs, crypto, and modern asset classes
- · Academic rigor — Princeton professor, decades of research
- · Strongest single defense of low-cost index investing in print
− Cons
- · Some technical jargon — slower reading than Bogle
- · Skip the first 100 pages on stock-picking history if pressed for time
Price, availability, and ratings can change; verify details on the retailer page before buying.
For first-time index investors, Bogle’s Little Book is the starter (1 weekend). Add the Bogleheads’ Guide for tactical implementation. Malkiel is for the year-2 investor who wants the deepest academic backing for their VOO holdings.