Bid, ask, and the spread
Learn what the bid, the ask, and the bid-ask spread really are, and why the spread is a cost you pay every time you enter and exit a trade.
Part of the Market Mechanics: Orders and Execution track on Agenticks. About 8 minutes, written for a intermediate reader.
When you glance at a quote, it is easy to assume there is one price for an asset, a single number that everyone trades at. There isn't. At any moment there are really two prices: the most a buyer will pay, and the least a seller will take. The single price you see on a ticker or a headline is usually just the price of the last trade that happened, not the price you can get right now. Almost everything about getting in and out of a position lives in the gap between those two live numbers, and learning to read them is one of the first things that separates a careful trader from someone who keeps getting surprised by their fills.
The bid is the highest price a buyer is currently willing to pay. The ask (sometimes called the offer) is the lowest price a seller is currently willing to accept. The bid is always lower than the ask. If a buyer were willing to pay what a seller wanted, the trade would simply happen and the quote would move on. Here is the part that catches new traders off guard. When you buy at market, you usually pay the ask. When you sell at market, you usually receive the bid. You are not trading at some single middle price. You are crossing from one side to the other.
The spread is a cost you pay to cross
The bid-ask spread is the gap between the bid and the ask. If you buy at the ask and immediately sell at the bid, you lose the spread even if the price never moved. That is why the spread is a real, built-in cost on every round trip, not just a number on the screen.
A simple example makes it concrete. Say a stock shows a bid of 100.00 and an ask of 100.05. The spread is 5 cents. Buy at market and you pay 100.05. Sell at market a second later and you get 100.00. You are down 5 cents per share before the market has done anything at all. On one share that is nothing. But think about what happens as you scale. Across a hundred shares that is five dollars, and across many trades a day it becomes a number that quietly shapes your results. This is also why the spread matters far more to an active trader than to someone who buys and holds for years. If you make one trade a decade, the spread is a rounding error you will never notice. If you take ten round trips a day, you cross that gap twenty times a day, and the spread becomes one of the largest recurring costs you face, often bigger than commissions. The more often you trade, the more the spread decides whether an idea that looks good on paper actually survives in practice.
Spreads are not fixed, and that is the part worth internalizing. They depend heavily on liquidity, which is how easily an asset trades without moving its price. A heavily traded, liquid market has many buyers and sellers stacked close together, so the spread is tight, often a penny or less. A thin or fast-moving market has fewer orders resting near the current price, so the spread widens, sometimes dramatically. The same asset can have a one-cent spread in the middle of a busy session and a much wider one in the quiet hours. Spreads also tend to widen around news releases, at the open and the close of the session, and any time volume dries up. That is exactly when many traders feel the urge to act quickly, so it is worth knowing that the cost of crossing the spread is often highest in the very moments that feel most urgent. A limit order, which lets you name your price instead of taking whatever is on offer, is one common way traders try to avoid paying a wide spread, though it comes with its own tradeoff of possibly not filling at all.
Spread and slippage are not the same thing
The spread is the known gap between bid and ask before you trade. Slippage is when your fill comes in worse than the price you expected, usually because the quote moved or your order was large enough to walk through several levels. A wide spread makes slippage more likely, but they are two separate costs.
You place a market order to buy. Which price do you generally pay? The ask A market buy crosses the spread and takes the lowest price a seller will accept, which is the ask.
- Bid
- Highest price a buyer will pay right now
- Ask
- Lowest price a seller will accept right now
- Spread
- The gap between the bid and the ask
- Liquidity
- How easily an asset trades without moving price
ask bid spread
Put the steps of a market round trip in order, and watch where the spread gets paid.
- See a quote with a bid below the ask
- Buy at market and fill at the ask
- Sell at market and fill at the bid
- Notice you lost the spread even with no price move
You can read a two-sided quote
You now know that the bid and ask are two different prices, that buying takes the ask and selling takes the bid, and that the spread is a real cost you pay on every round trip.
Common questions
- Is the spread really a cost if no fee shows up?
- Yes. The spread is a hidden cost because you usually buy at the higher ask and sell at the lower bid. Even with no commission listed, that gap is money you give up on a round trip.
- Why are some spreads wider than others?
- Spreads are tighter in liquid markets with many active buyers and sellers, and wider in thin or fast-moving markets where fewer orders are resting near the current price.
- Does the spread change during the day?
- It can. Spreads often widen around news, at the open and close, and in low-volume sessions, then tighten again when activity is steady and liquidity returns.
Terms defined in this lesson
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