How Index Funds Work

What an Index Is

A market index is a measurement of a segment of the stock market. The ASX 200 measures the 200 largest companies listed on the Australian Securities Exchange by market cap. The S&P 500 measures the 500 largest US-listed companies. These indices are calculated and maintained by index providers (S&P Global, MSCI, FTSE Russell) who define the rules for inclusion and weighting.

Indices are not investable directly — they're just numbers. Index funds (and index ETFs) are investment vehicles designed to replicate the index as closely as possible.

How the Fund Works

When you invest $10,000 in VAS (a fund tracking the ASX 300), the fund manager:

• Takes your money and buys shares in the 300 companies on the ASX in the same proportions as the index
• Issues you units in the fund representing your ownership stake
• When companies pay dividends, the fund collects them and distributes to unit holders
• When the index changes (a company joins or leaves, or weightings shift), the fund rebalances mechanically

You never pick stocks. The fund owns everything in the index. Your return equals the index return minus the fund's expenses (the MER).

Why Low Fees Matter So Much

The fee difference between index funds and active funds compounds brutally over time:

The maths is brutal because fees compound. A 1.13% annual fee difference doesn't take 1.13% of your outcome — it takes 23% of it over 30 years. This is why every dollar of fees matters.

Why Index Funds Outperform Most Active Managers

This is counterintuitive: if you have a team of expert analysts, how can you underperform a mechanical index? The answer is: markets are highly competitive. Every fund manager is competing against every other fund manager plus algorithmic traders, hedge funds, and informed insiders. The collective wisdom of all these participants is already priced into every stock.

The evidence is substantial. SPIVA (S&P Indices vs Active) reports that over 15 years, roughly 90–95% of Australian active equity fund managers underperform their benchmark index after fees. Selecting an outperforming manager in advance is essentially impossible — past performance doesn't predict future performance.

Index Funds vs ETFs

In Australia, the terms are often used interchangeably but there's a technical distinction:

• Unlisted index managed funds (like Vanguard's wholesale funds) are priced once daily at end-of-day NAV. Minimum investments can be $5,000–$500,000. Best for large regular investments, no brokerage.
• Index ETFs trade on the ASX during market hours at real-time prices. Minimum investment is the price of one unit (often $50–$150). Pay brokerage per trade. More flexible, slightly higher cost for small regular contributions.

For most Australians building wealth through a broker, index ETFs (VAS, VGS, A200) are the practical choice. For very large amounts or inside institutional structures, unlisted index funds may be preferable.

Tax Treatment in Australia

• Distributions: Taxed as income at your marginal rate. Australian index funds distribute dividends including franking credits.
• Capital gains: Tax only applies when you sell. Hold for 12+ months for the 50% CGT discount.
• Inside super: Returns taxed at 15% accumulation (0% in pension phase) — significantly more efficient for high earners.
• No internal CGT drag: Index funds trade less than active funds, realising fewer internal capital gains that flow through to investors as taxable events.