Realized spread: the cost that actually got paid
Posted: Fri Oct 30, 2026 2:40 pm
Realized spread: the cost that actually got paid
The quoted spread is a snapshot. The realized spread is what a round trip cost: entry at the ask, exit at the bid, minus whatever the price did in between.
To isolate the cost, compare each fill with the mid-price at the time of the fill. Entry cost is the difference between the fill and the mid. Exit cost is the same measure. Their sum is the realized spread, including any slippage.
Averaged over many trades, it shows the true cost of doing business. It often exceeds the quoted average, because trades cluster in busy moments, when spreads are larger and slippage more likely.
A strategy that trades during news or at the open pays a higher realized spread than the daily average suggests. The quoted figure on the website describes a different day than the one actually traded.
The comparison between brokers should be made on this basis: same strategy, same hours, realized cost. A broker with a lower headline spread can lose to one with a higher spread but better fills.
The measurement needs a reference mid-price series, which a tick recording provides.
Quoted average spread versus realized spread: how big is the gap in the journal?
The quoted spread is a snapshot. The realized spread is what a round trip cost: entry at the ask, exit at the bid, minus whatever the price did in between.
To isolate the cost, compare each fill with the mid-price at the time of the fill. Entry cost is the difference between the fill and the mid. Exit cost is the same measure. Their sum is the realized spread, including any slippage.
Averaged over many trades, it shows the true cost of doing business. It often exceeds the quoted average, because trades cluster in busy moments, when spreads are larger and slippage more likely.
A strategy that trades during news or at the open pays a higher realized spread than the daily average suggests. The quoted figure on the website describes a different day than the one actually traded.
The comparison between brokers should be made on this basis: same strategy, same hours, realized cost. A broker with a lower headline spread can lose to one with a higher spread but better fills.
The measurement needs a reference mid-price series, which a tick recording provides.
Quoted average spread versus realized spread: how big is the gap in the journal?