Paying the spread on a cross versus trading its two legs

[Fairman]

Paying the spread on a cross versus trading its two legs

EURGBP is, in a sense, EURUSD divided by GBPUSD. You can trade it directly, or you can build roughly the same exposure by buying one major and selling the other in the right sizes.

Most traders never think about the second option, and for good reason. But it does raise a question about spreads that's useful to understand.

The spread on a cross is often wider than the spread on either major. That's partly because the cross has less direct liquidity and partly because the broker's liquidity providers are, in effect, pricing it from the two legs. When you trade the cross, you're paying one spread that already includes some of the cost of both majors.

Trading the two legs yourself means paying two spreads and two commissions. On a raw account with tight majors, the total can come out close to the cross spread, sometimes a bit lower, often a bit higher. On a standard account it's usually worse.

There are practical problems with doing it by legs. Sizing has to be calculated so the dollar exposure cancels. Margin is used on two positions instead of one. And both legs need managing, which is more than most scalpers want to deal with.

So for nearly everyone, trading the cross directly is the sensible choice. The useful part of the comparison is that it shows why a cross spread is the size it is, and gives you a way to judge whether your broker's cross pricing is fair. If the cross spread at your broker is much wider than the two leg spreads added together, the markup is on the cross itself.

The check takes minutes. Note the bid and ask on both majors and on the cross at the same moment, calculate the implied cross price from the legs, and compare it with what your broker is showing. The gap between the two is the cushion.

[Fairman]

The comparison changes during the day. In the London session, both majors are at their tightest and the cross usually is too. In the late New York and early Asian hours, the majors widen, and crosses often widen more than either leg. If you see a cross spread jump at those hours, it's normally because the broker is protecting itself on a thinner product. Logging the cross spread alongside the two leg spreads at a few fixed times each day for a week shows how your broker handles it. It's also a good way to spot when a broker is pricing crosses unusually wide compared with their own majors.

[FXS London Scalper]

Building EURGBP from two legs is a good thought experiment for understanding the spread. In practice the legs cost two spreads plus two commissions, and the cross is usually cheaper during London, when EURGBP is liquid. Outside London hours the situation can change, because EURGBP liquidity drops more than EURUSD and GBPUSD. That is when the cross spread widens most compared with its legs. Worth checking with your own broker at a quiet hour, the difference can be surprising.

[Fairman]

The yen crosses are a good test of this. EURJPY and GBPJPY are actively traded in their own right, so their pricing doesn't always look like a simple combination of the legs. Something like AUDNZD or CADCHF is further from the majors and its spread is much more obviously built from the legs plus a cushion. The more exotic the cross, the wider the gap between what the legs would cost and what the broker charges for the cross, which is useful to know before choosing which crosses to scalp. For those crosses the case for sticking to the majors gets stronger. A simple way to compare is to note the cross spread and both leg spreads at the London open on three or four mornings and see how big the cushion is on each cross you trade.

[Fairman]

Swap is another hidden piece. Holding two legs overnight means paying or receiving two sets of swaps instead of one. Usually that's close to the cross swap, but not always, because brokers set their swap markups per symbol. For a scalper who closes before rollover it doesn't matter. For anyone holding a cross position for a few days, it helps to check the swaps on the cross against the two legs, because the markup can end up larger than the spread over a longer hold. Some brokers also apply a triple swap on a different weekday for some crosses, which can surprise anyone holding into midweek.

[Fairman]

There's a correlation point as well. If you already hold a position in EURUSD and then open EURGBP, you've effectively added to the euro side of your exposure. Some traders get caught by this, thinking they've diversified when they've really doubled down on one currency. Breaking crosses into their legs, at least on paper, helps you see your true net currency exposure across all open trades. Some platforms and tools can show this directly, which saves doing the arithmetic yourself. It's a few minutes of work at the start of a session and can stop a lot of accidental doubling.