Definition — Trading fees are the various costs that can apply when you buy or sell a stock. Some are charged by the broker, some by exchanges or regulators, and some are built into the price itself. "Zero commission" rarely means zero cost — it just means one type of fee is waived.
The main types of trading cost
Costs come in a few buckets. Not all apply to every trade or every market:
Commission — a flat or per-share fee to place a trade. Many brokers now charge zero on U.S. stocks, but not all markets or products.
The bid-ask spread — a built-in cost paid through the price, not a line item. Wider in thin or volatile stocks.
Regulatory & exchange fees — small, statutory charges passed through to you, such as U.S. sell-side regulatory fees or Hong Kong's exchange and government levies.
Currency conversion (FX) — if you fund in one currency and trade in another, a conversion cost can apply.
Financing / margin interest — only if you trade on leverage; interest accrues on borrowed funds.
Other service fees — withdrawals, inactivity, market data, or paper statements, depending on the platform.
Commission isn't the whole story
A "free" trade can still be expensive if the spread is wide or the FX rate is poor. The honest way to compare platforms is total cost to round-trip a trade — buy and sell — including spread and conversion, not just the headline commission.
Market-specific costs to know
Different markets tax and charge trades differently:
U.S. stocks — small sell-side regulatory fees (SEC / FINRA), passed through.
Hong Kong stocks — stamp duty (a government tax), plus exchange and regulator levies and settlement fees.
These are set by governments and exchanges, not the broker, so they apply almost everywhere you trade those markets.
How to keep costs low
A few habits cut your real cost meaningfully:
Trade liquid stocks and ETFs to keep the spread tiny.
Use limit orders in thin or fast markets so you don't overpay the spread.
Batch trades instead of many tiny ones if per-trade fees apply.
Mind FX — fund in the currency you'll trade where you can.
On StableStock, you fund with stablecoins and trade real U.S. and Hong Kong stocks — check the fee schedule in-app for the exact costs that apply to your trades.
Takeaway: Real trading cost is more than commission — it includes the spread, regulatory and exchange fees, FX, and (if you use leverage) financing. Compare platforms on total round-trip cost, and use liquid names and limit orders to keep it down.
This article explains fee types in general and is not a quote of any specific platform's charges. Always check the live fee schedule before trading.
Next steps
What is the bid-ask spread? — The cost that's hidden inside the price.
Market orders vs limit orders — Choosing the order type that controls your cost.
The cost of leverage — How financing interest adds up (if you trade on margin).
