Synthetic cross prices reveal when a pair is out of line
Posted: Sat Oct 31, 2026 7:10 am
A cross rate like EURGBP can be computed from EURUSD and GBPUSD. Dividing the two gives a synthetic price, and the actual quoted EURGBP should sit very close to it. Gaps beyond the combined spread signal either stale quotes or a temporary dislocation.
Retail traders cannot arbitrage this, since the speed and cost needed are far beyond a retail account. But it still works as a diagnostic tool. A quote that sits several points away from the synthetic price is probably lagging, and trading it means taking a stale price.
Watching the gap also reveals which feed updates faster. If one pair consistently catches up after the others move, that is where the lag lives, and the stale side is worth avoiding.
Building the synthetic price takes a few lines in most platforms. Plot the difference as an indicator and notice how it behaves in different conditions.
Does the gap between synthetic and quoted crosses show up in your data, and how large does it get during fast markets?
Retail traders cannot arbitrage this, since the speed and cost needed are far beyond a retail account. But it still works as a diagnostic tool. A quote that sits several points away from the synthetic price is probably lagging, and trading it means taking a stale price.
Watching the gap also reveals which feed updates faster. If one pair consistently catches up after the others move, that is where the lag lives, and the stale side is worth avoiding.
Building the synthetic price takes a few lines in most platforms. Plot the difference as an indicator and notice how it behaves in different conditions.
Does the gap between synthetic and quoted crosses show up in your data, and how large does it get during fast markets?