Choosing a broker — the costs that depend on how you invest

A per-trade commission is a fixed cost on a variable amount, so its percentage impact is set entirely by your order size. Two euros on a €2,000 purchase is 0.1%; the same two euros on a €100 purchase is 2%. An investor contributing monthly is paying the second rate, and no ongoing charge difference between funds comes close to mattering by comparison.

The practical consequence is that contribution frequency is a cost decision, not just a habit. Buying quarterly rather than monthly cuts the commission drag by roughly three quarters at the price of some time out of the market, and for small contributions that trade is usually worth making.

A percentage custody or platform fee behaves as the mirror image: irrelevant at small balances and dominant at large ones. A 0.25% annual platform charge on €10,000 is €25 a year, which a frequent trader would happily pay to avoid commissions. On €250,000 it is €625 a year — more than the ongoing charge of the entire portfolio, and paid for nothing but recordkeeping.

Because the two charges scale in opposite directions, the ranking of brokers reverses somewhere as a portfolio grows. That crossover point is worth locating rather than guessing, and it is the reason the broker you correctly chose when you started is often the wrong one a decade later.

The same fund is frequently listed on several exchanges in different currencies. Buying a dollar-denominated listing from a euro account means a conversion on the way in, on every dividend if it distributes, and again on the way out — often at a charge of around a tenth of a percent each time, quietly, without appearing as a separate line.

This is entirely avoidable by choosing a euro-denominated listing of the same fund, and it is one of the few costs on this page that can be eliminated rather than merely minimised. It is also the one most often invisible: nothing on the trade confirmation says "you could have avoided this".

Several brokers publish a list of funds tradeable without commission, sometimes with conditions attached — a minimum order size, a limit on frequency, or availability only on one exchange. A fund on that list can be materially cheaper to own than a fund with a lower ongoing charge that is not, particularly for a monthly investor.

Treat the list as a real input rather than marketing, and check the conditions rather than the headline. Also check whether the list is contractual or promotional: a fund that is free this year and not next changes the arithmetic after you have already bought it, and moving costs another round trip.

Investor protection schemes, whether assets are held in segregated custody or in a nominee structure, and where the entity is regulated are not costs, and they are not tie-breakers between reputable providers either — but they are worth reading once before committing a decade of savings. A broker outside your jurisdiction may also change your tax filing obligations, which is a real recurring cost in time even though it never appears in a fee table.

Execution quality, interface and reliability matter too, and cannot be usefully quantified here. The argument of this page is narrower: that the quantifiable part of the decision depends on your own behaviour, and that comparing tariffs without first describing how you invest produces a confident answer to the wrong question.

Which broker is cheapest?

The question has no answer without knowing how often you buy, how much you hold, and in which currency the listing is denominated. A commission-free platform with a percentage custody fee wins decisively for a small frequent investor and loses decisively for a large passive one. The comparison tools on this site take those inputs because there is no way to produce an honest ranking without them.

Should I move brokers to save on fees?

Compute the round trip first. Transferring in kind avoids selling but often carries a per-position fee; selling and rebuying means crossing the spread twice, paying commission twice, and in several countries realising a taxable gain that would otherwise have been deferred. A saving of thirty euros a year is a real saving, and it is not worth a one-off cost of several hundred.

Does it matter which exchange I buy on?

It matters for two reasons. The listing currency determines whether you pay a conversion charge, which is avoidable. And liquidity differs between listings of the same fund, so the spread you cross can differ even though the underlying assets are identical. Both favour the most liquid listing denominated in your own currency, where one exists.