Where the money quietly goes

What this is about

The costs of investing are individually small enough to ignore and collectively large enough to decide the outcome. They are also the part of the result you have the most influence over.

The four you pay

The spread. At any moment there is a price to buy and a slightly lower price to sell. The difference is a cost you pay the instant you enter, before the position has done anything. It is rarely itemised on a statement, which is why people believe "commission-free" means free.

Commission. The explicit one, and the only one that usually appears on a statement. Whether it is large or small relative to the others depends entirely on your broker and the size of your trades.

Slippage. The price you get is not always the price you saw, particularly in thinly traded shares or in a fast market. A market order asks for now and accepts whatever now costs.

Tax. Depends entirely on where you live and what account you hold. Selling at a profit is frequently a taxable event. Holding often defers tax on gains — but income from a holding, dividends and distributions, is commonly taxable as it arrives.

Why small becomes large

Costs do not simply subtract. They compound — because money paid away is money that does not earn anything afterwards.

The mechanism, stated plainly: if you trade at a steady rate, your per-trade costs amount to a recurring annual drag — and a portfolio growing at some rate minus a recurring cost does not just end lower. The shortfall grows as a share of what you would otherwise have had, every year without exception, because each year's cost comes out of a base that would have grown, and that missing growth is itself missing the year after.

(In absolute terms the gap widens while the portfolio grows. It is the proportional loss that always increases.)

Worked through: 100 growing at 7% a year for twenty years reaches about 387. The same 7% with 1.5% a year taken out compounds at 5.5% and reaches about 292 — roughly a quarter of the ending value gone, from a cost most people would call small. Those rates are an illustration, not a claim about your account.

This is why cost is the part of the argument that favours acting less often: the arithmetic is the same for everyone, whatever else differs about their situation.

The part people miss

Three of these four — spread, commission and slippage — are paid per transaction. Tax is not: capital gains are usually assessed on net realised gains across a tax year, and dividend tax is not tied to any trade at all. So cost is not a fixed property of investing — it is a function of how often you act. Two people who own the same shares for the same decade can have very different results if one of them rearranged the portfolio forty times along the way.

Two more the list above leaves out

Currency conversion. Buying shares priced in another currency usually costs a conversion fee each way, and for someone buying foreign shares it is often the largest single cost of the trade.

Transaction taxes. Some markets levy a duty on purchases — UK stamp duty on share purchases is the common example. It is paid on the way in, whatever happens next.

What this does not tell you

Cheapest is not always right. A cheap venue with poor execution can cost more in slippage than it saves in commission. The total is what matters, and the total is harder to see than the headline.

Tax rules are local, and holding is not automatically untaxed. Dividends and distributions are commonly taxable even when you sell nothing, and some places tax holdings or unrealised gains directly. Nothing here is tax advice. How your account is treated where you live is yours to check, or to take to someone qualified.

And low cost does not rescue a bad plan. Minimising cost on a strategy that does not work only means losing money more efficiently.

Where to see this in the app

Your Trade log lists every fill. The count itself is the number this lesson is about: multiply your typical position size by your round-trip cost, then by that count, and you have a figure most people have never worked out.