Table of Contents
Before answering how do index funds work, we have to understand what is index fund. An index fund is a type of investment tool. A mutual fund or exchange-traded fund (ETF) are also some tools of investment. These tools aim to replicate the performance of a specific benchmark index, such as the example index funds S&P 500. Investment in index funds is achieved by holding all, or a representative sample, of the securities in the index in the fund’s portfolio. According to Morningstar, as of 2021, there are about 3,500 index funds available for investment, covering a wide range of markets and investment strategies.
One of the key benefits of investing in index funds is their low costs and diversification. According to a 2020 report by the Investment Company Institute, the average expense ratio for index funds was 0.09%. The expense ratio is 1.25% for actively managed funds. When investors invest in index funds, they save a significant amount in fees over time, which can have a significant impact on their returns.
Index funds are considered ideal core portfolio holdings for retirement accounts such as individual retirement accounts (IRAs) and 401(k) accounts.
Well known and noted investor Warren Buffett has recommended index funds as a haven for savings for the later years of life. In a 2016 letter to shareholders, he stated “Both large and small investors should stick with low-cost index funds.”
He has said, it makes more sense for the average investor to buy all of the S&P 500 companies at the low cost that an index fund offers, rather than picking out individual stocks for investment.
How do Index Funds Work?
Index funds are a form of passive investment, where the fund manager builds a portfolio that mirrors the securities of a particular index. Instead of actively stock picking and market timing, the fund manager aims to match the performance of the index.
There are a wide range of indexes and index funds available for investment, covering various markets and sectors. In the United States, the most well konwn and noted index funds track the S&P 500 index. However, other commonly used indexes include:
- The Wilshire 5000 Total Market Index, which is the largest U.S. equities index
- The MSCI EAFE Index, which consists of foreign stocks from Europe, Australasia, and the Far East
- The Bloomberg U.S. Aggregate Bond Index, which follows the total bond market
- The Nasdaq Composite Index, made up of 3,000 stocks listed on the Nasdaq exchange
- The Dow Jones Industrial Average (DJIA), including 30 large-cap companies
For example, an index fund tracking the DJIA would invest in the same 30 large publicly-owned companies that make up the index. The portfolios of index funds only change appreciably when their benchmark indexes change. If the fund is following a weighted index, its managers may timely readjust the percentage of different securities to reflect the weight of their presence in the benchmark.

Index Funds vs. Actively Managed Funds
As we have understood, Index funds are a form of passive investing, where the portfolio is constructed to match the performance of a specific market index, such as the S&P 500. In contrast, actively managed mutual funds employ a strategy of securities selection and market timing, where portfolio managers make individual stock picks and try to outperform the market. According to a study by Morningstar, Inc., an investment research firm, in 2020, passively managed funds, such as index funds, accounted for an estimated 42% of assets under management in the United States, while actively managed funds made up the remaining 58%.
Lower Costs
One of the primary advantages that index funds have over actively managed funds is their lower management expense ratio (MER). The MER is a measure of the total costs associated with running a fund, including things like advisor and manager fees, transaction costs, and accounting expenses. Because index fund managers simply aim to replicate the performance of a benchmark index, they don’t need the same level of staff or resources as actively managed funds, which translates to lower costs for investors.
According to a study by Morningstar, Inc., the average MER for passive funds is 0.25%, while the average MER for active funds is 1.25%. This means that investors in index funds can save up to 1% annually in management costs compared to those in actively managed funds.
But it’s not all serious business, you can always add a bit of fun to your investment choices. As the famous investor Warren Buffett once quipped, “I will tell you how to become rich. Close the doors. Be fearful when others are greedy. Be greedy when others are fearful.”
Better Returns?
- Advocates suggest that passive funds have been successful in surpassing most actively managed mutual funds.
- According to data from S&P Dow Jones Indices, during the five-year period ending Dec. 31, 2020, approximately 75% of large-cap U.S. funds manifested into a return that was less than that of the S&P 500.
- On the other hand, passively managed funds do not try to beat the market. Their strategy instead try to match the overall risk and return of the market, on the theory that the market always wins.
- The positive performance of Passive management tends to be true over the long term.
- With shorter time spans, active mutual funds perform better. The SPIVA Scorecard shows that in a span of one year, only about 60% of large-cap mutual funds underperformed the S&P 500.
- In other categories, actively managed money rules. For example, more than 86% of midcap mutual funds outperform their S&P MidCap 400 Growth Index benchmark in the span of a year.
Example Index Funds
- Index funds have been around since the 1970s, but have seen a surge in popularity in the 2010s due to the appeal of low fees and a long-running bull market.
- According to Morningstar Research, in 2021, investors poured more than $400 billion into index funds across all asset classes, while actively managed funds experienced $188 billion in outflows.
- The Vanguard 500 Index Fund, pioneered by Vanguard chair John Bogle in 1976, is one of the best for its overall long-term performance and minimum cost.
- The Vanguard 500 Index Fund tracks the S&P 500 faithfully, in composition and performance.
- As of Q2 2022, Vanguard’s Admiral Shares (VFIAX) generated an average 10-year cumulative return of 237% % vs. the S&P 500’s 238.1%, showing a very small tracking error.
- The expense ratio is 0.04%, with minimum investment of $3,000.
- Example index funds are SPDR S&P 500 ETF (SPY), iShares Russell 2000 ETF (IWM) and iShares MSCI EAFE ETF (EFA).

How Do Index Funds work {Exchange-Traded Funds (Index ETFs) }?
- Index funds may be organized as exchange-traded funds (index ETFs)
- Index ETFs are actually portfolios of stocks that are managed by a professional financial firm.
- Every unit share represents a small ownership stake in the entire portfolio of index ETFs.
- The aim of the financial firm managing an index ETF is not to exceed the underlying index, but simply to match its performance.
- For example, if a particular stock makes up 1% of the index, then the firm managing the index ETF will seek to mimic that same composition by making 1% of its portfolio consist of that stock.
Do Index Funds Have Fees?
- Yes, index funds have fees, but they are generally much lower than those of actively managed funds.
- Many index funds offer fees of less than 0.2%
- On the other hand, active funds often charge fees of more than 1%.
- The difference in fees can have a significant impact on investors’ returns when compounded over longer time frames.
- This is one of the primary reasons why index funds have become such a popular investment option in last few years.
Are Index Funds Better Than Stocks?
- Index funds track portfolios consistingof many stocks.
- As a outcome, investors benefit from the positive effects of diversification, such as:
- Increasing the expected return of the portfolio
- Minimizing the overall risk
- While some individual stock may observe its price drop steeply, if it is just a relatively small component of a larger index, it would not be as damaging.
Are Index Funds Good Investments?
While understanding how do index funds work, many experts agree that index funds are very good investments for long-term investors. They are pocket friendly options for getting a well-diversified portfolio that passively tracks an index. Don’t forget to compare different index funds or ETFs to be sure you are tracking the best index for your financial goals and at the lowest cost as per your need.