Index funds have become, over the last decade, one of the most popular investment tools among small savers, thanks to a combination of simplicity, diversification, and low fees. Understanding their basic logic helps you decide whether they fit your savings strategy.
What an index fund is
It's an investment fund whose goal isn't to beat the market through active management decisions, but to replicate the performance of a benchmark stock market index (for example, the S&P 500 in the United States, or global indices grouping thousands of companies from around the world), by buying the same assets that make up that index in the same proportions.
Active management vs. passive management
- Active management: a management team decides which assets to buy and sell, trying to beat the market through analysis and stock picking. This generally comes with higher management fees to compensate for that work.
- Passive management (index funds): there's no active stock picking; the fund simply replicates an existing index. Since it doesn't require a team of analysts making constant decisions, management fees tend to be considerably lower.
Why low fees matter so much over the long run
A fee difference that looks small in the short term (say, 1.5% versus 0.2% a year) has a huge cumulative effect over several decades, precisely because of the same mechanism behind compound interest: every percentage point that goes to fees is a percentage point that stops compounding, year after year, on your capital.
Automatic diversification as an added advantage
By replicating a broad index, an index fund gives you exposure, in a single transaction, to hundreds or thousands of different companies, achieving a level of diversification that would be very costly and complex to replicate by buying individual stocks one by one.
Index funds don't eliminate market risk
It's important not to confuse "diversified" with "risk-free": an index fund remains fully exposed to overall market risk. If the index it tracks falls, the value of your investment falls in the same proportion, with passive management offering no additional protection against those declines.
Index funds vs. ETFs: a common distinction
ETFs (exchange-traded funds) are, in many cases, also index funds, but they differ in how they're traded: an ETF is bought and sold on the stock exchange just like a share, while a traditional index fund is subscribed to and redeemed directly through the management company, with a single net asset value calculated at the close of each trading session. Both share the same philosophy of tracking an index with low fees.
Model the effect of long-term returns
Our compound interest calculator lets you project how your investment would evolve under different assumptions about average annual returns, useful for getting a sense of the cumulative effect of investing consistently over many years.