The headline spread on a broker’s marketing page is not what you pay to trade. The real number is the all-in round-trip cost — spread plus commission plus slippage — and two accounts advertising “tight spreads” can cost wildly different amounts once you total it up.
Three cost models you’ll actually meet
Every account bills execution in one of three ways. Knowing which one you’re on is the first step to costing a trade honestly.
- Spread-only. No separate commission. The broker’s fee is baked into a wider spread — the gap between bid and ask. You “pay” it by entering slightly against yourself and needing price to move a little further before you break even. Common on standard forex accounts and most CFD accounts.
- Raw-spread + commission. The broker passes through a near-interbank raw spread (sometimes fractions of a pip) and charges an explicit commission per lot per side. This is the typical ECN / raw model.
- Commission-only / fixed-fee. Common in futures, where you trade a centralised exchange price and pay a flat commission (plus exchange and clearing fees) per contract per side. The spread is whatever the order book shows, not a broker markup.
None of these is automatically cheaper. A tight raw spread with a fat commission can beat or lose to a wider all-in spread depending on the instrument and your size. You have to add it up.
The round-trip cost of a single trade
Round-trip cost is what it costs to open and close one position — the number that actually comes out of your account.
Break it into its parts:
- Spread cost = the bid/ask gap you cross on entry, valued in your account currency for your position size.
- Commission = per-side charge × 2 (you pay it entering and exiting).
- Slippage = the difference between the price you wanted and the price you got, worst around news and on thin books. Real, and easy to ignore because it never appears as a line item.
Add those three and you have the honest cost of the trade. That total is the hurdle every trade has to clear before the first cent of profit — and it’s why your risk-to-reward has to be measured on net prices, not the clean entry and exit you imagined. If a setup targets a modest reward, run it through the risk-reward calculator using fills after cost; a 1.5R idea can quietly become a 1.2R idea once the round trip is paid.
How costs scale with frequency and size
Cost is not a fixed tax — it scales along two axes, and both compound.
Frequency. Round-trip cost is paid per trade. A swing trader taking a few positions a week pays it a handful of times; a scalper taking dozens of trades a day pays it dozens of times. Same per-trade cost, radically different monthly total. The more trades your edge needs, the more your edge has to beat cost just to stand still.
Size. Spread and commission both scale with lots or contracts. Double your size, double the cash cost of the round trip. That’s fine when the edge is real — but it means costs grow exactly in step with the size you add when you’re trying to hit a profit target, so they eat into the target you were scaling up to reach.
The trap is that neither axis hurts on any single trade. It’s the aggregate over a month that decides whether your strategy is viable. That’s an argument for measuring realised cost per strategy rather than eyeballing it — Shibiki’s auto-journaling logs the actual fees and fill quality on every trade, so your recorded expectancy is net of what execution really cost, and the live edge health read (with its Wilson confidence interval) tells you whether a high-frequency strategy is genuinely profitable after the drag or just busy.
Comparing brokers on all-in cost, not headline spread
To compare two accounts honestly, convert everything to a single number: all-in round-trip cost per standard unit (per lot in forex, per contract in futures), in your account currency.
- Take the typical spread during the sessions you actually trade — not the best-case number in the ad, and not the news-spike number either.
- Add commission for both sides.
- Add a realistic slippage estimate for your style.
- Multiply out to your normal position size and compare like with like.
Do this per instrument, because the ranking flips: a broker that’s cheapest on EUR/USD can be expensive on gold or an index. And do it for the sessions you trade, since spreads widen outside a pair’s core hours.
For futures traders, the comparison is a little cleaner — the exchange price is common to everyone, so you’re mostly comparing commission per contract and execution quality across platforms like Tradovate and cTrader. On a prop evaluation, also confirm how your firm accounts for commissions and fees against your target and drawdown; the specifics differ, so check directly with the firm, whether that’s Topstep or another.
Why cost hits scalpers hardest
Cost is a fixed toll per trade; profit target is variable. Put those together and the pattern is obvious.
A scalper aims for a few ticks or pips per trade and takes many trades. If the round-trip cost is, say, a meaningful fraction of that target, then a large slice of every winner is gone before it’s booked — and every loser is that much larger. Trade the same edge less often, for a bigger target, and the same absolute cost becomes a rounding error. That’s the core reason high-frequency styles are the most cost-sensitive: they have the least room per trade to absorb the toll and pay it the most times.
The practical takeaways for a cost-heavy style:
- Trade the tightest-cost instruments in your setup’s universe, and trade them during their liquid hours.
- Demand more reward per trade than your instinct says, so cost is a smaller share of the target.
- Measure net, not gross. Judge the strategy on realised expectancy after every fee — which is exactly the number Shibiki keeps for you.
Related: Risk-reward calculator · cTrader integration · Topstep