Bid-Ask Spread

Bid-Ask Spread

The bid-ask spread is the gap between two prices quoted for any tradable asset at a given moment: the bid, which is the highest price a buyer is currently willing to pay, and the ask (or offer), which is the lowest price a seller is currently willing to accept. The formula is simple: spread = ask price - bid price. Because the two sides rarely match exactly, this gap exists continuously in almost every market, from stocks and bonds to forex and commodities, and it is quoted alongside the last traded price on virtually every trading platform. The size of the spread tells you something important about the asset. A narrow spread, often just a fraction of a percent, usually signals a liquid, heavily traded market where buyers and sellers are plentiful and prices move in small increments. A wide spread signals the opposite: fewer participants, lower trading volume, or greater uncertainty about the asset's fair value. Traders often express the spread as a percentage of the midpoint price — (ask - bid) divided by the average of ask and bid, times 100 — which makes it easier to compare spreads across assets priced very differently. It's worth remembering that the bid-ask spread is not a fee charged by your broker; it exists in the market itself, set largely by market makers and dealers who quote both prices. When you buy at the ask and immediately sell at the bid, the spread is the cost you absorb, separate from any commission. For active or frequent traders, spread costs can add up meaningfully over time, so it pays to be aware of typical spreads for the assets you trade.

Example

Suppose you pull up a real-time quote for a large, actively traded U.S. stock and see a bid of $174.98 and an ask of $175.02. The bid-ask spread here is $175.02 - $174.98 = $0.04. As a percentage of the midpoint price of $175.00, that works out to ($0.04 / $175.00) x 100 = about 0.023%. This is a very tight spread, typical of a heavily traded large-cap stock where thousands of shares change hands every second and many market participants are competing to buy and sell. Now compare that to a thinly traded small-cap stock quoted at a bid of $12.10 and an ask of $12.45. The spread is $12.45 - $12.10 = $0.35, and as a percentage of the $12.275 midpoint, that's ($0.35 / $12.275) x 100 = about 2.85% — more than a hundred times wider in percentage terms than the large-cap example. If you bought 1,000 shares at $12.45 and immediately sold at $12.10, you would lose $350 purely to the spread, even before any commission, simply because the stock trades so much less actively.

Practical Application

Retail and institutional investors use the bid-ask spread as a quick gauge of trading cost and liquidity before placing an order, especially for less common stocks, options, or exchange-traded funds. A wide spread on an ETF, for example, might prompt an investor to use a limit order rather than a market order, so they don't accidentally buy at an inflated ask price or sell at a depressed bid. Market makers and dealers are on the other side of the spread: they continuously quote both a bid and an ask, profiting from the difference in exchange for standing ready to buy or sell at any time. This compensates them for the risk of holding inventory in a fast-moving market and for the possibility of trading with better-informed counterparties, known as adverse-selection risk. In foreign exchange trading, the bid-ask spread is central to how brokers earn revenue, since many forex brokers charge no separate commission and instead build their profit into the spread on currency pairs. Traders comparing brokers or currency pairs — say, EUR/USD versus an exotic pair like USD/TRY — will typically find the major, highly liquid pairs carry far tighter spreads.

Common Mistakes

A common misconception is treating the bid-ask spread as a fee charged by the broker. In reality, it's a market-wide phenomenon set by supply and demand and by market makers' quotes, not a line item your brokerage bills you for separately, even though it functions as a real cost to you as a trader. Another mistake is confusing a wide spread with high volatility. While the two are often related, they measure different things: volatility describes how much a price swings over time, while the spread describes the gap between the best buy and sell quotes at a single moment. An asset can have a wide spread with modest volatility simply because it trades infrequently. Traders who trade in and out of positions frequently sometimes underestimate how much cumulative spread cost erodes returns, particularly with less liquid securities or during volatile market conditions when spreads tend to widen. Over dozens or hundreds of trades, spread costs can rival or exceed commissions. Finally, some assume a narrow spread by itself guarantees a good, low-risk trade. A tight spread reflects good liquidity at the very top of the order book, but it says nothing about how much volume is available beyond that top price — a large order can still move the market significantly even in a nominally 'tight' market.

Comparison