Education

Understanding the Bid-Ask Difference in a Stock

By Walid Mograbi · 2026-06-09 · 2 min read

The bid-ask spread is the hidden cost behind every stock order. Learn how Ask and Bid define the real entry and exit level, and how spread size reflects liquidity, risk, and execution quality.

From Price Quote to Execution Cost

The market quote shows two key numbers at the same time: **Ask** and **Bid**. The gap between them is the practical cost you pay for executing a stock trade quickly.

Key definitions

• **Ask** (offer): the lowest price a seller agrees to accept now.
• **Bid**: the highest price a buyer agrees to pay now.

These are the prices currently available in the live order book, not a prediction of where the stock “should” go.

How market orders are filled

For a **market buy**, you are typically filled near the Ask. For a **market sell**, you are typically filled near the Bid. So one trade executes at one side of the quote and another side handles the opposite direction.

Why this gap is the spread

The difference between Ask and Bid is called the **spread**. That spread is a real execution cost that appears immediately when you trade at market pace, even before commissions or fees are considered.

Example from a quick quote

• Ask = 20.20
• Bid = 20.00
• Spread = 0.20

A fast buy may be filled around **20.20**, while a fast sell may clear around **20.00**. That 0.20 is the cost embedded in timing and liquidity for that moment.

Practical checklist before placing a stock order

• Check the current spread size before placing each market order.
• Compare it to recent levels for the same stock.
• Be extra careful with large sizes if the spread is wide or changing fast.
• Treat narrow spreads as usually better execution conditions.

Core benefit and warning

When you measure spread per trade, you stop reacting to one single price and start trading the **full execution reality**.

**Warning:** in volatile periods, spread can widen quickly. Large market orders can become expensive and less predictable.