The Case for Passive Investing
Decades of research consistently show that most actively managed funds fail to outperform their benchmark index over the long term, especially after fees are accounted for. This insight gave rise to passive investing — a strategy of tracking a market index rather than trying to beat it. The two most popular vehicles for passive investing are Exchange-Traded Funds (ETFs) and index funds. They're often confused for the same thing, and while they share a core philosophy, there are important practical differences.
What Is an Index Fund?
An index fund is a type of mutual fund designed to replicate the performance of a specific market index — such as the S&P 500, FTSE 100, or MSCI World. You invest a set amount of money, and the fund manager uses it to buy all (or a representative sample) of the securities in that index, in the same proportions.
Index funds are priced once per day, after the market closes. You buy and sell at that end-of-day price, called the Net Asset Value (NAV).
What Is an ETF?
An Exchange-Traded Fund also tracks an index, but it trades on a stock exchange just like an individual share. This means you can buy and sell an ETF at any point during the trading day, and its price fluctuates in real time based on supply and demand.
ETFs can track stock indices, bond indices, commodities, sectors, or even specific investment strategies — making them an extremely versatile tool.
How They Compare
| Feature | Index Fund | ETF |
|---|---|---|
| Trading | Once daily (end-of-day NAV) | Throughout the trading day |
| Minimum investment | Often a fixed minimum (e.g., $1,000) | As low as one share (or fractional) |
| Expense ratios | Low, sometimes matching ETFs | Generally very low |
| Transaction costs | Usually none (direct from provider) | Brokerage commissions may apply |
| Tax efficiency | Good | Generally slightly better |
| Accessibility | Through fund provider | Through any brokerage |
Which Is Better for Long-Term Investors?
For most long-term, buy-and-hold investors, the differences are minor. Both give you broad market exposure at low cost. However, here's a rough guide:
Choose an index fund if:
- You invest a fixed amount regularly (e.g., monthly contributions) and want to automate without worrying about share prices
- You prefer simplicity and don't want to think about bid-ask spreads
- You're investing through a 401(k) or pension scheme where ETFs may not be available
Choose an ETF if:
- You want flexibility to start with a small amount
- You're investing via a brokerage that doesn't offer mutual funds
- You want access to more specific themes or asset classes
- Tax efficiency is a priority in a taxable account
The Importance of Expense Ratios
Whichever you choose, always check the expense ratio — the annual fee charged as a percentage of your investment. Even small differences compound significantly over decades. A fund charging 0.03% annually is vastly more beneficial long-term than one charging 0.50%, all else being equal. Look for funds from well-established low-cost providers and compare total costs before committing.
The Bottom Line
Both ETFs and index funds are excellent, low-cost tools for building long-term wealth through passive investing. The "best" choice depends on how and where you invest, not on any inherent superiority of one structure over the other. In many portfolios, both have a role to play.