Index funds are the most boring investment vehicle ever invented, and they consistently outperform the most exciting ones over long periods. Here is why, and how to use them.
What an Index Fund Is
An index fund tracks a defined basket of securities — the S&P 500, the total US stock market, a global bond index. It is not trying to "beat" anything. It owns everything in the index in proportion, charges almost nothing, and earns whatever that market segment earned.
Why They Win
SPIVA's annual research consistently shows that over 15-year periods, more than 85% of active US-equity funds underperform their benchmark index after fees. Lower costs compound just like returns — except in your favor.
A Three-Fund Portfolio
The most popular index portfolio holds: a US total-market fund, an international total-market fund, and a US bond fund. Pick weights based on your age and risk tolerance. That's the entire decision.
How Much to Hold in Each
Common starting points:
- 20s–30s: 80–90% stocks, 10–20% bonds
- 40s: 70/30
- 50s: 60/40
- 60s+: 50/50 or more conservative
Within stocks, US vs international is typically 70/30.
Costs to Watch
The Vanguard, Fidelity and Schwab broad-market index funds charge between 0.00% and 0.04%. Anything above 0.20% should make you skeptical.
Bottom Line
Pick three low-cost index funds, set automatic monthly contributions through a DRIP-enabled brokerage account, rebalance once a year using our Portfolio Rebalancing Calculator, and let time do the work.
Frequently Asked Questions
Why do index funds tend to outperform actively managed funds over time?
Index funds simply hold all the securities in a target index rather than trying to pick winners, which keeps costs extremely low, and lower costs directly translate into higher net returns over time. Long-running industry research has found that over 15-year periods, a large majority of actively managed U.S. equity funds have underperformed their benchmark index after fees. Past performance doesn't guarantee future results, but the cost advantage of index funds is structural and persistent.
What is a three-fund portfolio?
A three-fund portfolio combines a U.S. total-market stock fund, an international total-market stock fund, and a U.S. bond fund, with the specific weightings adjusted for an investor's age and risk tolerance. It's one of the most popular index-investing structures because it provides broad diversification with minimal complexity. As with any investment strategy, it does not eliminate market risk or guarantee a positive return.
How should stock and bond allocations change with age in an index portfolio?
A common starting framework allocates roughly 80–90% to stocks and 10–20% to bonds in your 20s and 30s, gradually shifting toward around 50/50 or more conservative by your 60s and beyond. This general glide path reflects a typically longer time horizon and higher risk tolerance earlier in life, though individual circumstances can justify a different mix. This is a general guideline, not personalized advice, so investors should weigh their own goals and risk tolerance.
Run the numbers yourself
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