Among the many types of index funds available, total market index funds occupy a particularly notable position, aiming to capture essentially the entire investable stock market in a single holding, rather than focusing on a narrower slice like only large companies or a specific sector. Understanding why this genuinely broad approach appeals to so many long-term investors reveals some compelling, well-supported reasoning.

What Makes a Fund “Total Market”

A total market index fund tracks an index specifically designed to include the vast majority of a market’s investable securities across the full range of company sizes, from large, well-established companies down to smaller, less established ones, rather than concentrating exclusively on a narrower segment like only the largest companies in a market.

How Total Market Differs From Large-Cap-Only Indexes

Fund Type	Coverage
Large-cap index fund	Primarily the largest companies in a market
Total market index fund	Companies across the full range of sizes — large, mid, and small

While large-cap indexes capture a significant portion of total market value, given how much larger companies tend to weigh in market capitalization terms, a total market fund captures meaningfully more individual companies and market segments, including smaller companies that a large-cap-only fund would entirely exclude.

The Diversification Argument

Total market index funds offer some of the broadest diversification available in a single investment product, spreading risk across an enormous number of individual companies and market segments, meaning the poor performance of any single company or even an entire sector has a comparatively smaller impact on the fund’s overall performance than it would in a more narrowly focused holding.

Why Some Investors Prefer This Over Selecting Multiple Narrower Funds

1. Simplicity — a single total market fund automatically provides broad diversification without requiring you to separately select and maintain proper proportions across large-cap, mid-cap, and small-cap funds individually
2. Automatic rebalancing within the fund — as company sizes and market segments shift in relative value over time, the total market index automatically adjusts its composition accordingly, without requiring any action on your part
3. Reduced risk of unintentional gaps — building your own combination of narrower funds carries some risk of unintentionally overweighting or entirely missing certain market segments

Historical Performance Considerations

Over long time periods, total market index funds have generally captured the broad market’s overall return, including contributions from smaller company growth that a large-cap-only approach might miss during periods when smaller companies happen to outperform larger ones, though this relationship can vary considerably across different specific time periods.

Using a Total Market Fund as a Single Core Holding

Given their broad diversification and low cost, many investors use a single total market index fund as the core, foundational holding of their entire equity portfolio, sometimes even as close to their sole equity holding, reflecting a genuinely simple, “one-fund” approach to capturing broad stock market exposure.

Combining Total Market Funds With Additional Diversification

While a total market fund provides broad domestic diversification, some investors choose to supplement it with additional international market exposure, bond fund holdings for asset class diversification, or other specific allocations, building a more complete overall portfolio around the total market fund as a strong, broad foundation rather than a complete, standalone solution.

Cost Considerations for Total Market Funds

Total market index funds are generally available at very low expense ratios, similar to other broad passive index funds, reflecting the same mechanical, rules-based tracking approach that keeps costs low across the broader index fund category, making this broad diversification available at minimal ongoing cost.

Who Total Market Funds Tend to Suit Well

Total market index funds tend to particularly suit investors seeking a genuinely simple, low-maintenance approach to broad equity market exposure, those building a long-term portfolio around a small number of core, well-diversified holdings, and anyone who prefers not to make ongoing decisions about specific market segment weightings themselves.

Frequently Asked Questions

Is a total market index fund better than a large-cap-only index fund?

Neither is universally “better” — a total market fund provides broader diversification across company sizes, while a large-cap fund concentrates specifically on larger, more established companies; the right choice depends on your specific diversification preferences and investment goals.

Can I use a total market index fund as my only investment?

Some investors do use a single total market fund as their primary or sole equity holding, reflecting a genuinely simple approach, though many also choose to supplement it with international exposure, bond holdings, or other asset classes for additional diversification within their overall portfolio.

Do total market funds include international companies?

Generally no — most total market index funds track a specific country’s total market, such as the total U.S. stock market, requiring a separate international fund if you want exposure to companies outside that specific home market.

How is a total market index fund different from an S&P 500 index fund?

An S&P 500 fund tracks a specific index of approximately 500 large U.S. companies, while a total market fund includes a considerably broader range of companies across all size segments, including many smaller companies the S&P 500 index doesn’t include at all.

Final Thoughts

Total market index funds offer a genuinely compelling combination of broad diversification, simplicity, and low cost, capturing the full range of company sizes within a market rather than concentrating exclusively on the largest companies alone. For investors seeking a straightforward, low-maintenance core holding for their equity portfolio, this broad approach provides a well-supported, evidence-based foundation worth serious consideration.