The Real Cost of a Forex Trade: Spread and Swap

Step 4 of 4 in Forex Essentials.

Forex is advertised as commission-free, which is true in the narrow sense that many brokers charge no explicit fee. The costs are still there — folded into the spread you cross on entry and exit, and into the swap you pay for every night the position stays open.

Both are small per trade and neither is optional. Over a year they are often the difference between a profitable strategy and a flat one.

Spread: paid on every trade

The spread is the gap between bid and ask. You buy at the ask and sell at the bid, so a position is underwater by the spread the instant it opens.

Spread cost = spread in pips × pip value

One standard lot of EUR/USD with a 1.2-pip spread:

1.2 × $10 = $12 per round trip

Twelve dollars sounds trivial. Multiply by frequency:

On a $10,000 account, 100 trades a month at a 1.2-pip spread costs 12% of the account per month in friction. The strategy has to clear that before it earns anything.

Spread relative to the stop is what matters. A 1.2-pip spread against a 100-pip swing stop is 1.2% of the risk — negligible. The same spread against an 8-pip scalping stop is 15% of the risk, on every single trade. Tight stops and wide spreads do not coexist profitably.

Spreads also widen exactly when you least want it: at the rollover hour, around data releases, and on exotic pairs. A pair quoted at 1.2 pips in London can be 6 pips during the Asian session.

Swap: paid on every night held

Every currency has an interest rate. Holding a pair means holding one currency long and the other short, and you receive or pay the difference, adjusted by the broker's own markup. This is the swap (or rollover), applied at 5pm New York.

Swap cost = swap in pips per night × pip value × nights

One standard lot charged 0.8 pips per night, held ten nights:

0.8 × $10 × 10 = $80

Three details catch people out:

• Wednesday counts triple. Spot forex settles two business days forward, so the Wednesday rollover carries the weekend — three days of swap in one charge. A position held over Wednesday costs more than one held over Saturday.
• Swap can be positive. Long a high-rate currency against a low-rate one and you may be credited. That is the carry trade — though brokers' markups mean the credit is usually smaller than the rate differential suggests.
• It is direction-specific. The swap on long EUR/USD and short EUR/USD are different numbers, not mirror images, because the markup is applied to both.

Slippage: the cost nobody quotes

The third cost has no line on any statement. Slippage is the gap between the price you expected and the price you got — market orders in fast conditions, stops triggered in a gap, entries during a news spike.

Under normal conditions it averages a fraction of a pip and cuts both ways. Around events it is one-directional and can be many pips. There is no formula; the only way to know yours is to log expected versus filled price on every trade and take the average.

Putting the three together

Express total cost as a fraction of the risk on the trade, and compare it against expectancy:

Cost per trade in R = (spread + slippage + swap ÷ trades) × pip value ÷ risk amount

A swing strategy risking $100 per trade, paying 1.2 pips of spread and 0.5 of slippage on 0.3 standard lots:

1.7 pips × $3 = $5.10, or 0.05R

Against an expectancy of 0.35R, that is 15% of the edge — acceptable. Against an expectancy of 0.08R it is more than half, and the strategy is mostly working for the broker.

Reducing it

• Match the account type to the frequency. Raw-spread plus commission usually wins above roughly 20 trades a month; all-in spreads win below it. The table above shows how close the two are — run it with your own numbers.
• Trade the liquid sessions. London and the London–New York overlap have the tightest spreads. The same setup taken at 3am costs materially more.
• Use limit orders where the strategy allows. Entering on a limit means the market comes to you, and the spread is not crossed on entry.
• Avoid holding through Wednesday on strategies with thin edges, or size the expected triple swap into the plan.
• Count costs before judging a strategy. A backtest without spread, swap and slippage is not a backtest of anything you can trade.