Index funds and passive investing

Passive investing means buying a fund that tries to copy a market index rather than one that tries to beat it. An index fund holds the same securities as its chosen index, in the same proportions, and simply tracks it. The appeal is low cost and simplicity: nobody is being paid to pick winners, so the running cost is small.

What an index is, and how a fund tracks it

A market index is a defined, rules-based list of securities meant to represent a slice of the market — say the largest listed companies, or a particular segment. An index fund buys those same securities in those same weights, so its holdings are decided by the index’s rules rather than by a manager’s judgement. When a company enters or leaves the index, the fund adjusts to match. That is the entire job.

Passive versus active

An actively managed fund pays a manager and a research team to choose holdings in the hope of doing better than the market. A passive fund gives up that attempt and settles for matching the index at low cost. The trade is straightforward: active investing offers the possibility of beating the index and the possibility of trailing it, at a higher cost; passive investing removes both possibilities and the higher cost, aiming only to match. Which is right for you is a judgement, not a fact, and neither is universally better.

Why passive usually costs less

Because no one is being paid to select securities, a passive fund’s expense ratio is typically far lower than a comparable active fund’s, and regulation caps it lower too. Cost is one of the few things about a fund you can know in advance rather than hope for, which is a large part of why passive investing has grown.

Tracking error: the small gap

A passive fund never matches its index perfectly. The small gap between the fund’s result and the index’s is called tracking error, and it comes from costs, cash held for redemptions, and the timing of adjustments. A well-run index fund keeps tracking error small; a large one means the fund is not doing its one job well. It is the number to look at when comparing two funds tracking the same index.

Where it fits

Passive funds are a low-cost way to own a broad slice of the market without having to judge a manager, which is why many people use them as a core holding. They still carry full market risk — an index fund falls when its index falls, in full, because tracking the index means tracking it down as well as up. Passive or active is a choice about cost and belief, not about safety; the market risk is the same either way, and it sits within the broader picture of equity, debt and hybrid holdings.