The Full Picture of Transaction Costs — Visible Costs and Hidden Costs
Do you think the only cost of buying and selling a stock once is "a few hundred won in commission"? In fact, larger costs may be leaking out where you cannot see them.
Transaction Costs Split into Two Kinds
Transaction costs are broadly divided into "explicit" and "implicit" costs.
Explicit costs are visible costs you can know in advance. Brokerage commissions, the securities transaction tax, and various regulatory fees fall here. Think of them as the costs printed on a receipt.
Implicit costs are hard to see and hard to measure. The difference between the buy and sell quotes (the bid-ask spread), the market impact of your order pushing the price up, and the opportunity cost from not being able to buy at the moment you wanted, all fall here.
The larger the amount traded (like institutional investors), the more often implicit costs become far larger than explicit costs. Explicit costs stand out and get a lot of attention, but they are often only a small part of the total transaction cost.
Explicit Costs: What Gets Printed on the Receipt
Taking Korean stocks as an example, brokerage commissions have often dropped to the 0.01% range (or below, through promotions) on a non-face-to-face basis. But the securities transaction tax charged when selling (0.15% for KOSPI and KOSDAQ as of 2025) takes up a far larger share than the commission.
For overseas stocks, brokerage commissions tend to be higher than domestic ones (for example, roughly 0.07–0.25% in the case of U.S. stocks), on top of which the FX conversion spread and local regulatory fees are added. Just because it is "explicit" does not mean it is all small.
Commission rates and transaction tax rates change frequently with brokerages, promotions, and tax-law revisions. You should check the actual numbers in your own account's fee schedule.
Implicit Costs: More Dangerous Because They Are Hidden
The bid-ask spread is the difference between "the price at which you can buy right now" and "the price at which you can sell right now." If you resell immediately after buying, you lose exactly this difference on the spot. For actively traded large-cap stocks this difference is very small, but for thinly traded stocks it is large, and a single round trip alone can make a few percent disappear.
Market impact is the cost of your order itself moving the price. If you try to buy a large quantity all at once, the price gets pushed up, and you end up filling at a higher price than the one that first appeared.
The Lesson for Long-Term Investors
A transaction cost may look small "for one trade," but it accumulates the more often you buy and sell. The higher the turnover (trading frequency), the more both explicit and implicit costs grow, eating into your return no matter how good the stock you picked.
The attitude this site emphasizes, "good assets, held for a long time, steadily," is also reasonable from the standpoint of transaction costs. Simply reducing the number of times you buy and sell lets you save on the visible commissions and the invisible spread and impact costs at the same time.
Preguntas frecuentes
Q. If there is a commission-free promotion, is the transaction cost zero?
No. Even if the brokerage commission is zero, other costs such as the securities transaction tax on selling, the bid-ask spread, and market impact remain. "Free" removes only part of the explicit cost, and the implicit costs still occur.
Q. Do individual investors need to worry about implicit costs too?
For small trades in large-cap stocks, the spread is small and may not be a big burden. But if you frequently trade thinly traded small-caps or newly listed stocks, the spread and slippage can accumulate surprisingly, so caution is needed.
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