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Investing · 3 min read

What is an index fund?

A fund that aims to match a market index by holding its investments, or a representative sample of them, at low cost.

In plain words

One company in the market index that Priya's index fund follows goes out of business, and its shares end up worth nothing. Her fund loses that one slice. It still holds every other company in the index, so the loss is only a small part of what she owns.

People meet index funds when reading an investment account’s fund choices or a workplace savings plan. They may also see them in fund factsheets that show what the fund owns and the fee it charges.

A yearly fee is taken from the whole pot each year, so it can reduce future growth too. A small-looking fee can grow into a large cost over time.

Mei's fund has grown over the year, so the fund company takes its fee from the pot. The fee is a slice of everything she has in there, so a bigger pot means a bigger fee. Her balance is lower by that slice, and she never writes a cheque.

Knowing this helps you see how fees can shrink long-term growth, even when funds earn the same market return. Missing it can leave you with less money because higher fees compound over time.

Two worked examples

US
An index fund at 0.1% a year vs an active fund at 1%: on the same 7% market return that is ≈29% more money after 30 years.
Japan
An index fund at 0.1% a year vs an active fund at 1.5%: on the same 5% market return that is ≈50% more money after 30 years.

The common mistake

The mistake: Expecting a broad fund to beat the market, when its job is to match it cheaply.

What’s true: An index fund spreads your money across many investments and aims to match the market cheaply. An active fund pays a manager to pick winners, like choosing a few runners instead of joining the whole race. A common mix-up is expecting an index fund to beat the market; its job is to match it cheaply, not win by guessing.

Asset allocation

Your mix of stocks and bonds usually matters more to long-term results than picking one stock over another. It is like choosing the road before worrying about which car to take. A common mistake is choosing the mix because it did best last year, even though the time your money can stay invested matters more.

You meet this idea when choosing how much of your savings goes into stocks or bonds. It also appears when a workplace plan or investment service asks about how long your money can stay invested.

Where you’ll meet it

  • A yearly fee compounds against youEach year's fee also removes the growth that money would have earned in every year after.
  • Time is the strongest dialRate and contribution have ceilings; starting earlier multiplies both and costs nothing.
  • No return without riskThe extra return is payment for stomaching the swings — remove the swings and the pay disappears.

Related terms

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Education, not financial advice Source: Theorise lesson and coach text