India, Nov. 4 -- A currency pair can look calm for hours and then become noticeably more expensive to trade within seconds. The reason is often the forex spread: the gap between the bid price available to sellers and the ask price available to buyers. When that gap widens, a trader pays more to enter the market even if the underlying exchange rate has barely moved.

This matters most around the moments that already dominate financial news: inflation reports, central-bank decisions, employment data, political developments, and unexpected market shocks. Price direction gets most of the attention, but the quality of the quote can change just as quickly.

A currency quote is really two prices

Forex screens normally show a bid and an ask rath...