Trading Costs Explained: Spread, Commission, Fees
Every trade starts slightly behind. The spread, commission and financing costs are small per trade and decisive over time — and they apply whether you win or lose.
Costs are the least glamorous part of trading and among the most important. They are easy to ignore because each one looks trivial, and ruinous precisely because they compound on every trade, in every direction. A trader who understands costs has an edge over one who chases gains while leaking capital through fees they never counted.
Where this sits in the trade
This is the cost layer that presses on every stage of the lifecycle in the mechanics. It builds on the spread introduced in the order, and pairs with the foundations references on slippage and spread and reading a broker fee schedule.
The cost stack
The spread. The gap between the bid (sell) and ask (buy) price. You cross it the instant you trade, so you begin every position at a small loss equal to the spread. Tighter spreads (major currency pairs, large shares) cost less; wider spreads (small or volatile instruments, quiet hours) cost more. For "commission-free" brokers, the spread is often where the cost is hidden.
Commission. A direct fee per trade, charged by some brokers (commonly on shares) instead of, or alongside, a spread mark-up. "Zero commission" rarely means zero cost — it usually means the cost has moved into the spread or into other charges.
Overnight financing (swap). For leveraged positions held past the daily cut-off, you pay a financing charge — interest on the borrowed portion of the position. On a CFD or spread bet held for weeks, this can quietly become the largest cost of all, and it is why leveraged products suit short holding periods far better than long ones.
The quieter charges. Currency-conversion fees (trading an instrument priced in another currency), inactivity fees, withdrawal fees, and data or platform fees. Individually minor; collectively a drag, especially on a small account.
Why small costs decide outcomes
Costs are corrosive because they are certain and repeated. A strategy that wins slightly more often than it loses can still lose money once the spread is paid on every entry and exit. The more frequently you trade, the more times you cross the spread and pay commission, so high-frequency approaches must clear a far higher bar just to break even. And because financing accrues daily, a leveraged position that drifts sideways for a month can lose money purely to carrying cost, even if the price never moves against you.
The practical lesson is not "avoid all costs" — it's that costs are a permanent headwind that any approach must overcome before it makes a penny, and they are one reason the retail-loss reality from the mechanics is so persistent.
The jurisdiction lens
The structure of costs is universal, but two things differ by jurisdiction. First, tax can act like a cost: UK share purchases attract Stamp Duty Reserve Tax, which Australian share purchases do not — a difference covered in the products. Second, disclosure rules differ: UK firms must present costs under Financial Conduct Authority (FCA) rules, and Australian firms under Australian Securities and Investments Commission (ASIC) rules, while an offshore platform may disclose far less. Always read the full fee schedule for the account you actually hold.
The case for and against worrying about costs
For. Costs are the one part of trading you can measure precisely and control directly. Choosing tighter-spread instruments, trading less often, and reading the fee schedule are reliable improvements that require no market view at all — pure, controllable edge.
Against. Cost-cutting can be taken too far: chasing the lowest headline spread onto an unregulated platform trades a small saving for a large risk, and obsessing over fractions of a pip can distract from the far bigger risks of leverage and position sizing. Costs matter, but they are not the largest danger in the room.
No verdict — know your costs precisely, then weigh them against the risks that can do far more damage.
FAQ
What is the bid-ask spread? The difference between the price you can sell at (bid) and buy at (ask). You pay it the moment you open a trade, so every position starts slightly in the red.
Is "commission-free" trading really free? Rarely. The cost usually moves into a wider spread or into other charges such as currency conversion or financing. Read the full fee schedule rather than the headline.
What is overnight financing? A daily interest charge on the borrowed part of a leveraged position held past the cut-off. Over weeks it can become the biggest single cost, which is why leveraged products suit short holds.
Do trading costs really matter that much? Yes. Because they apply to every trade in both directions and compound over time, they can turn a marginally winning approach into a losing one — especially with frequent trading.
What it connects to
Costs are a steady drain; leverage is what turns a drain into a flood. The next piece covers the single mechanic most responsible for large retail losses. Continue to The Leverage: how borrowing to trade magnifies losses (Piece 4).
This article is general information only and is not financial advice or a recommendation to trade or to use any product or platform. [Publication] is not a licensed financial adviser. Trading and investing carry risk, including loss of capital; leveraged products such as CFDs and spread bets can lose money rapidly, and most retail accounts lose money. Figures are accurate as of June 2026 and will change. Rules, taxes, products and protections differ by country — do your own research and consider a locally regulated professional.
Sources: FCA (cost disclosure, COBS), ASIC (fee disclosure), gov.uk / HMRC (Stamp Duty Reserve Tax), broker fee schedules. Top-level resources; verify tax and disclosure detail at publish.