Bid-Ask Spread

The Bid-Ask Spread is the difference between the highest price a buyer is willing to pay (Bid) and the lowest price a seller is willing to accept (Ask) for a particular asset, such as a cryptocurrency. The Bid-Ask Spread is an important concept in trading as it represents the cost of trading a particular asset. When a trader executes a market order to buy, they pay the ask price; when they sell, they receive the bid price. The difference between these two prices — the spread — represents an implicit cost that the trader incurs on every round-trip transaction, even before accounting for exchange fees.

The size of the bid-ask spread is a direct measure of a market's liquidity. Highly liquid markets with many active buyers and sellers, such as the BTC/USDT pair on a major exchange, typically have very tight spreads, sometimes just a fraction of a percent. Less liquid markets, such as obscure altcoins or pairs on smaller exchanges, can have spreads of several percent, meaning traders start each position at a significant disadvantage. For algorithmic strategies that involve frequent trading, operating in tight-spread markets is essential for profitability.

Market makers — traders who place both buy and sell limit orders continuously to provide liquidity — profit from the bid-ask spread by collecting the difference between the price they buy at and the price they sell at. Bots are particularly effective at market making because maintaining tight, responsive quotes on both sides of the order book requires constant monitoring and rapid order updates that are impractical to perform manually. Understanding and accounting for the bid-ask spread is a fundamental requirement for any algorithmic trading strategy, as ignoring it can turn a theoretically profitable strategy into a loss-making one in live trading.