Returns are uncertain but costs are certain. The layers of trading costs, the truth about zero commission, what 1% does over time and how to tally a year.
Nobody knows what you will earn, but costs leaving on every trade is certain. Managing the controllable cost before the uncontrollable return is therefore the rational order. The more often you trade, the more this certain loss accumulates.
Counting only the commission shown on screen misses the real cost. A single round trip carries several items.
Charging no commission still leaves the difference between the buying and selling price. That difference is a real cost and widens in thinly traded assets. Commission waivers also usually carry a period or conditions, so checking the rate after they end is worthwhile.
Where gains are taxed, selling crystallises the tax each time. Holding the same asset longer defers the tax to that later point, and the deferred amount keeps working in the meantime. Frequent trading removes that effect. Rates and allowances vary by country and by year, so check the current rules.
A 1% annual cost difference looks small over one year. Subtracting 1% every year from the same return, though, visibly separates the final amount over a long period. That is why comparing products means looking at total expenses and trading costs rather than expected return alone. This explains the structure of costs and recommends no particular product.
If you have no feel for how much costs add up to, the surest way is to calculate them from the past year's trades. Total the amount bought and sold over the year and multiply by the round-trip commission rate plus any tax charged on sales. Spreads and slippage are harder to measure precisely, but comparing the quoted price at order time with the actual fill on a handful of trades gives a rough size. Divide the total cost by your average invested capital to get an annual cost rate. Frequent traders are often surprised by how large this figure is. Downloading your broker's annual statement makes it easier.
Funds and exchange-traded products you don't trade yourself still have costs. The most visible is the total expense ratio: management, distribution and custody fees drip out of the assets a little every day. Because they are already reflected in the net asset value rather than charged to your account separately, they are hard to feel. Beyond that are trading costs inside the fund, the spread when buying and selling listed products, and in some funds, sales charges and redemption fees. If the product documents show a figure for total actual costs in addition to the expense ratio, check that too.
The most direct way to cut costs is to trade less, and the effective way to do that is to reduce what triggers trades in the first place. You can set purchase and review dates and not place orders in between, or use a rule that rebalances only when weights drift outside a set range. Limit orders instead of market orders can reduce spread and slippage, though you must accept that they may not fill. Thinly traded stocks cost more to trade, so if two products serve the same purpose, choosing the more actively traded one helps. This guide explains cost structure and does not recommend any trading method.
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