Every stock has two prices at once — one to buy and one to sell. The gap between them is the bid-ask spread, a small but constant cost that quietly shapes every trade.
At any instant a stock has a bid — the highest price a buyer is willing to pay — and an ask (or offer) — the lowest price a seller will accept. The bid is always lower than the ask. The difference between them is the bid-ask spread.
Suppose the bid is $99.95 and the ask is $100.05. If you buy immediately you pay the ask ($100.05); if you sold right back you'd get the bid ($99.95). You're instantly down $0.10 a share before the price moves at all. That round-trip loss is the spread, and it's how the spread acts as a hidden transaction cost on every trade.
A market maker is a firm that quotes both a bid and an ask all day, profiting from the spread thousands of times over while keeping the market liquid. They take on the risk of holding inventory in exchange for that tiny, repeated edge.
Feel the spread from the other side: quote your own bid and ask around a moving fair price in the market-making drill and learn why too-wide quotes win no trades.
Not advice: educational content with simulated prices. For official basics see investor.gov.
See where the spread fits in how the stock market works, and look up bid, ask and liquidity in the trading glossary.
It is the difference between the bid (the highest price a buyer will pay) and the ask (the lowest price a seller will accept) for a stock at a given moment.
Because you buy at the higher ask price and sell at the lower bid price. The gap between them is an immediate loss on any round-trip trade, acting as a hidden transaction cost.
Highly liquid, heavily traded stocks have narrow spreads, often a penny. Thinly traded, volatile, or after-hours stocks have wider spreads because fewer buyers and sellers are available.
Market makers do. They continuously quote both a bid and an ask, earning the small spread many times over while providing liquidity to the market.