Definition — Every tradable stock shows two prices: the bid (the highest price buyers are currently willing to pay) and the ask (the lowest price sellers are willing to accept). The gap between them is the bid-ask spread — and it's a real, if hidden, cost of trading.
Bid, ask, and the spread
Think of a marketplace: buyers shout the most they'll pay, sellers shout the least they'll take. A trade happens when those two prices meet.
Bid — the best price you can sell into right now.
Ask — the best price you can buy at right now.
Spread — ask minus bid. The narrower it is, the cheaper it is to get in and out.
If a stock is "1.00 / 1.02", you'd buy at 1.02 and could immediately sell at 1.00 — a 0.02 spread you effectively pay to round-trip.
Why does the spread exist?
The spread is the reward for whoever provides liquidity — market makers and other traders posting orders. It compensates them for the risk of holding inventory and standing ready to trade. In effect, the spread is the price of immediacy: the cost of being able to trade right now instead of waiting.
What makes a spread wide or narrow?
Spreads aren't fixed — they widen and narrow with conditions.
Spreads are narrow when:
The stock is heavily traded (high liquidity).
Many buyers and sellers are active.
The market is open and calm.
It's a large, well-known company or broad ETF.
Spreads are wide when:
The stock is thinly traded.
Few orders are posted.
It's pre-market, after-hours, or volatile.
It's a small, obscure, or news-driven name.
Why the spread matters to you
The spread is part of your trading cost, even when commissions are zero. In liquid stocks it's tiny and easy to ignore. In thin or volatile names it can be larger than any commission — and it's a major reason a market order can fill at a surprising price.
On StableStock, you can see the live bid and ask before you trade, and use limit orders to avoid paying more of the spread than you intend.
Takeaway: The bid-ask spread is the gap between the best buy and sell prices — a hidden cost that rewards liquidity providers. It's small in liquid stocks and wide in thin or volatile ones. Watching the spread helps you avoid overpaying for immediacy.
Next steps
What is slippage? — The spread is one of its biggest causes.
Market orders vs limit orders — A limit order lets you sidestep part of the spread.
What is liquidity? — Why some stocks have tight spreads and others don't.
