Index funds and mutual funds, side by side

Start with the two words, because the confusion is entirely in the language.

Mutual fund describes a structure. Money from many people is pooled, a single portfolio is bought with it, and each holder owns a proportional slice. It says nothing at all about what is inside or how the holdings were chosen.

Index fund describes an instruction. The fund must hold whatever a published index says to hold, in the stated weights, and must not exercise judgement. It says nothing about the legal wrapper the fund arrives in.

So an index fund is very often a mutual fund. Asking which is better is like asking whether a paperback is better than a mystery novel.

The category error in the question

The comparison people actually mean is index tracking against active management, and that is a real question with a real answer structure. It is worth insisting on the precise version, because the vague version leads people to believe they are choosing between two shelves when they are choosing between two instructions.

Structure and strategy, on one grid

Two questions are being asked at once, and they are independent of each other. What legal wrapper does the fund arrive in, and what instruction does it follow once it is running.

The wrapper affects how you buy and sell, how prices are struck during the day, and some administrative detail. The strategy and the cost affect what you end up with. Beginners are routinely encouraged to spend their attention on the first column of that distinction and almost none on the second.

What an index fund is actually doing

An index is a published list with rules: which holdings are in it, in what weights, and when that changes. It is a measurement, maintained by whoever owns it, and it exists whether or not any fund tracks it.

A fund tracking that index has one job, and it is mechanical: hold what the list says, in the proportions the list says, and adjust when the list changes. There is no judgement to pay for, no research team to fund, and very little trading beyond what the rules force. That is why it is cheap. Not because of philosophy, but because following a rule is not expensive work.

Two honest limitations follow, and they are rarely stated by enthusiasts.

• An index is a choice, not neutrality. Somebody decided the rules, the weights and the boundaries. Tracking one is following that set of decisions rather than escaping decisions.
• Tracking is never perfect. Costs and timing create a small gap between the index and the fund, which is why the difference between them is a thing worth checking rather than assuming.

What you are paying for with active management

An actively managed fund employs people to decide what to hold, in the hope of beating a chosen benchmark. That is a real service and it costs real money: analysts, research, systems, and more trading, since decisions imply transactions.

The arithmetic to hold onto is simple and neutral. A fund charging more must produce more before costs simply to arrive at the same place as a cheaper fund. The difference is not a hurdle at the end; it is a subtraction every year, taken from a balance that was meant to be compounding.

This site takes no position on whether any particular manager is worth the fee, because that would be a recommendation and we do not make those. What we will do is show what the subtraction costs over a long holding period, since that part is arithmetic rather than opinion.

What one point of annual cost does

Sit with the scale of that. In the first year, the difference between the two costs is 70 dollars, which is nothing. Across twenty five years it becomes 8,122, because the amount taken out never gets the chance to compound, and neither does the growth it would have produced.

The same mechanism, run on contributions rather than a lump sum, is worked through in compound interest explained, where one percentage point over thirty years costs about 17,226 on 36,000 paid in.

How to read a fund in four numbers

Whatever wrapper it arrives in, four figures tell you most of what a beginner needs. They are on every factsheet, usually in that order of importance and inverse order of prominence.

Ongoing cost

The annual charge for holding it, as a percentage. Small numbers, compounded against you every year, as the table above shows.

What it holds

The actual contents and their concentration. A fund can hold hundreds of names while most of its behaviour comes from a handful of large ones, which matters for diversification.

Turnover

How much of the portfolio is bought and sold in a year. Trading has costs that sit outside the headline charge, so high turnover means the stated fee understates the total.

Benchmark and tracking

What the fund measures itself against, and how far it has diverged. A fund with no clear benchmark is a fund with no clear definition of success.

Notice what is not on that list: last year performance. It is the number printed largest and the one that tells you least, because it is simultaneously the most persuasive and the least predictive information available.

This page explains how fund costs and structures work in general. It names no fund, no provider and no index, contains no recommendation, and the percentages used in the arithmetic are illustrative values chosen to show a mechanism.