How To Find The Best Index Funds For Beginners

Ignore performance rankings and focus on two numbers: the expense ratio (under 0.10%) and the tracking error. The 'best' fund is the one that most cheaply and accurately mirrors its index, not the one that had the best year.

Why the best index funds keep costs low

Chasing last year’s top-performing index fund is a trap because past returns are often driven by sector flukes or temporary market anomalies that revert to the mean. A difference of even 0.50% in fees can erode tens of thousands of dollars over decades due to compounding. For example, a $10,000 investment as priced by the fund’s own prospectus on its most recent reporting date in a fund with a 0.03% expense ratio grows to roughly $57,000 over 30 years at 7% returns, while the same investment in a 0.50% fund yields only $51,000, a $6,000 penalty for doing nothing wrong. When you understand how often are mutual funds compounded, typically daily for most index funds, you realize that every basis point of fee drags down your balance with each compounding period. Low cost is the only performance predictor that reliably repeats.

The three numbers that actually matter

To filter out marketing noise and risky tiny funds, check only three metrics. First, the expense ratio: look under 0.10% for standard index funds, and under 0.20% for specialty ones. Second, the tracking error: this measures how closely the fund follows its index; a tracking error above 0.20% often signals hidden costs or poor replication. Third, assets under management (AUM): avoid funds with less than $500 million in AUM, a threshold set by the fund company and reported in its regulatory filings, as tiny funds can close or suffer from liquidity issues. These three numbers cut through the clutter of “top 10” lists. For deeper context on the broader category, the hub for this topic is funds & etfs, where you can compare these metrics across thousands of offerings without relying on hype.

When a popular index fund is a bad choice

A fund with a great brand name can still be a poor deal if it is a high-fee ‘closet index’ fund, an actively managed fund that mimics an index but charges 1% or more. Also, avoid ETFs with low trading volume and wide bid-ask spreads, which eat into your returns every time you trade. For instance, a well-known S&P 500 ETF with $2 billion in assets might seem safe, but if its average daily volume is below 10,000 shares, you could pay a spread of 0.50% per trade. If you want to buy mutual funds without a broker directly from a fund family, you avoid these spread costs entirely, but you must still check the fund’s expense ratio. Similarly, be wary of funds pushed by advisors: financial advisors get paid on mutual funds through 12b-1 fees or revenue sharing, which can push you toward a fund with hidden costs that undermine the index advantage.

Building your starter portfolio with two funds

Combine a total stock market index fund and a total bond market index fund to create a complete, self-balancing portfolio. Use a 90% stock / 10% bond split if you are young and risk-tolerant, or 80/20 for more stability. Rebalance once per year by selling what has grown and buying the laggard, which automatically locks in gains and buys low. Both funds should have expense ratios under 0.10% and tracking errors under 0.10%. This two-fund approach covers every U.S. stock and every investment-grade bond, giving you diversification without complexity. Avoid adding international or sector funds until you have at least $50,000 invested, a minimum portfolio size threshold set by the fund sponsor and verified in the current prospectus; the simplicity of two funds prevents the paralysis that sinks many beginners. With these two low-cost, accurate index funds, you have a portfolio that will beat most actively managed alternatives over any 20-year period.

The only reliable edge in index investing is paying the absolute minimum for exact replication, because every dollar saved in fees is a dollar that stays in your account and compounds for decades without any skill or luck required. For a deeper dive into the broader topic of funds & etfs: what to know and how to handle it, explore how these principles apply across the full landscape of investment vehicles.