S&P 500 or Total Stock Market Index Fund: Which Should I Buy?
Direct answer
S&P 500 vs total stock market index fund
They are very similar. An S&P 500 fund holds about 500 large companies covering roughly 80% of the US market's value; a total-market fund adds thousands of mid-size and small companies. Because large companies dominate both, returns have usually been close. Costs and simplicity matter more than the choice itself.
- S&P 500 ≈ 80% of available US market value
- Total-market funds add mid and small caps
- Both are market-cap weighted, so results are usually close
- Compare expense ratios
- avoid owning both by accident
On X this question usually shows up as two tickers: VOO or VTI. Those are just examples of two fund types that many providers offer. UXS does not recommend any particular fund; the question is about S&P 500 funds versus total-market funds in general.
What people on X are asking
One February 2026 thread called it "the most asked question in index fund investing": "Should I buy VOO or VTI?" The answers on X are almost unanimous that the difference is small, though posters disagree about whether small companies are worth including.
The fact-checked answer
S&P 500 funds. S&P Dow Jones Indices says the S&P 500 includes 500 leading US companies and covers about 80% of available US market capitalization.
Total-market funds. These track indices that include nearly every listed US stock, adding mid-size and small companies to the same large ones.
Why results are close. Both are weighted by market value. The large companies that make up about 80% of the US market are in both funds with similar weights, so the extra few thousand smaller stocks change results only modestly. In years when small companies beat large ones, total-market funds tend to do slightly better, and vice versa.
Diversification. Investor.gov describes diversification as spreading money across many investments to reduce risk. A total-market fund is slightly more diversified by company count, but both remain concentrated in the largest US firms and in one country.
Costs and structure. Investor.gov explains that index funds aim to match an index and that fees reduce returns. Broad index funds from major providers often have very low expense ratios; compare them for the specific funds available to you.
Comparison table
| Feature | S&P 500 fund | Total-market fund |
|---|---|---|
| Companies | About 500 | Thousands |
| Share of US market value | About 80% | Nearly 100% |
| Includes small companies | No | Yes |
| Overlap with the other | Very high | Very high |
| Typical cost | Low | Low |
Decision helper
| If you... | Consider |
|---|---|
| Want the simplest single US fund | Either; total market is the broader of the two |
| Already hold a separate small-cap fund | S&P 500 avoids double-counting small caps |
| Want to match the most common benchmark | S&P 500 |
| Are choosing for a retirement account | The one with the lowest cost available in your plan |
Checklist
- Check what you already own so you do not hold the same stocks twice.
- Compare expense ratios and minimums for the funds available to you.
- Decide whether you also want non-US stocks or bonds; neither fund includes them.
- Pick one and contribute regularly; switching back and forth costs more than the difference.
Common mistakes
- Holding both and thinking you are doubly diversified.
- Choosing on one or two years of performance differences.
- Forgetting international diversification entirely.
FAQ
Is a total market fund better than an S&P 500 fund?
Not clearly. It is broader, but results have usually been close because large companies dominate both.
Do I need both?
Usually not. They overlap heavily.
Which is safer?
Neither is safe in the sense of avoiding losses; both fall when the US market falls.
What about the Nasdaq-100?
It is more concentrated in large growth companies and swings more. See S&P 500 or Nasdaq-100.
ETF or mutual fund version?
ETFs trade during the day like stocks; mutual funds trade once a day at net asset value. Costs and account access matter more than the wrapper.
Does UXS recommend a specific fund?
No. We explain how fund types work; choose based on cost and your needs, or ask a licensed adviser.
Sources
- S&P Dow Jones Indices: S&P 500
- SEC Investor.gov: Index fund
- SEC Investor.gov: Diversification
- SEC Investor.gov: Exchange-traded fund (ETF)
Facts checked November 10, 2026. X posts are cited as evidence of the question, not of the answer.