Definition
The best ask, also called the best offer, is the first displayed price on the sell side. It identifies the cheapest visible supply on that venue at that instant. The accompanying size shows how much is offered at the price, potentially across several separate orders.
How It Works
A market buy generally consumes the best ask before moving to higher offers. For example, if 1 unit is offered at a hypothetical price of 101 and another 2 at 102, buying 2 units can cost 203 before fees, despite the best ask initially being 101. Larger orders therefore require depth beyond the top quote.
Key Considerations
The best ask can change between display and execution, and does not include every possible trading cost. It is distinct from a chart’s last trade and from the best bid. Subtracting the best bid from the best ask gives the quoted spread for the same market and observation time.