Stock index funds
Family I · Instruments
Not to be confused with index, limit stock order, index cfd.
Stock index funds are pooled investment vehicles designed to track a market index, such as the S&P 500 or FTSE 100, by holding the same securities in approximately the same weights. They offer broad diversification and typically have lower costs than actively managed funds because they do not require ongoing security selection. Shares of these funds trade on exchanges or are bought directly from the fund provider, depending on the structure.
Structure and replication methods
Index funds may be structured as mutual funds, exchange-traded funds (ETFs), or other collective vehicles. The manager can use full replication, holding every constituent in the index, or sampling, holding a representative subset when the index is large or illiquid. The objective is to minimise tracking difference, the gap between the fund's return and the index return, after accounting for fees and expenses.
Worked example: tracking an index
Suppose an index consists of two stocks, A and B, with market capitalisations of $800 and $200, giving weights of 80% and 20%. An index fund with $1,000 to invest buys $800 of A and $200 of B.
If the index rises by 5% and the fund's expenses are 0.1%, the fund's net asset value would increase by approximately 4.9%, assuming no tracking error from other sources.
Costs and considerations
Index funds typically have lower expense ratios than actively managed funds, but costs vary by provider, market, and fund size. Investors may also incur brokerage commissions when buying or selling ETF shares. Tracking error can arise from fees, cash drag, sampling, or changes in index composition. Tax treatment of dividends and capital gains distributions depends on the investor's jurisdiction and the fund's legal structure.
Often confused with
- index
- An index is a statistical measure of market performance, not an investable product, whereas a stock index fund is a vehicle that attempts to replicate that measure; the visible sign is that an index has no share price or expense ratio.
- limit stock order
- A limit stock order is an instruction to buy or sell a specific stock at a set price or better, while a stock index fund is a diversified portfolio; the visible sign is that a limit order is an action on a single security, not a holding.
- index cfd
- An index CFD is a contract for difference whose underlying reference is a stock market index, such as the S&P 500 or FTSE 100, and which settles in cash for the difference between the opening and closing prices without any exchange of the underlying basket of shares.