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The Bid-Ask Spread

The bid-ask spread is the gap between the highest price a buyer will pay (the bid) and the lowest price a seller will accept (the ask). This seemingly small difference—often just a penny or two—is a direct cost paid by every trader on every trade. Understanding the bid-ask spread is critical because it represents real money leaving your pocket every time you buy or sell. Over a lifetime of trading, spreads can cost thousands or even millions of dollars. The spread exists because markets need to balance the competing interests of buyers who want to pay less and sellers who want to receive more. Learning to calculate, anticipate, and minimize spread costs is one of the most practical skills in trading.

Quick definition: The bid-ask spread is the difference between the highest price buyers are willing to pay (bid) and the lowest price sellers are willing to accept (ask). It represents the cost of immediate execution.

Key takeaways​

  • The bid-ask spread is a direct cost paid by traders taking liquidity (submitting market orders)
  • Spreads are typically measured in basis points (a basis point is one-hundredth of a percent)
  • Wider spreads indicate lower liquidity or higher uncertainty; tighter spreads indicate abundant liquidity
  • Bid-ask spreads vary by time of day, market conditions, company size, and trading volume
  • High-frequency market makers profit by providing liquidity and collecting the spread
  • Institutional traders and retail traders can reduce spread impact through strategic order placement
  • During market stress and volatility, spreads widen dramatically as traders demand higher compensation for risk
  • The spread is not a fee charged by the exchange—it's the price of immediate execution

The Economics Behind the Spread​

The bid-ask spread compensates market makers for three things: the risk of holding inventory, the cost of providing liquidity, and the profit margin for their business. When a market maker posts a bid to buy at $100 and an ask to sell at $100.02, they're hoping to buy shares from one seller and sell them to another buyer, capturing the two-cent spread as profit.

But the market maker faces real risks. If they buy shares at $100 and the stock price falls to $99 before they find a buyer, they lose money. If they accumulate too many shares in one position, they have concentrated risk. The wider the spread, the more compensation the market maker is demanding for these risks. In a blue-chip stock like Microsoft, where the fundamental value doesn't change much minute to minute and countless traders are ready to trade, spreads are tight. In a speculative penny stock where value is uncertain and few traders are interested, spreads are wide. Market maker regulations are published by finra.org.

Calculating Your Spread Cost​

The spread cost is straightforward to calculate. If you submit a market order to buy 1,000 shares at the ask of $100.02 and simultaneously want to sell at the bid of $100.00, your round-trip spread cost is $20 (1,000 shares × $0.02 per share). If you execute many trades, these costs compound.

For a more sophisticated calculation, traders often measure spread as a percentage (in basis points). A basis point is 1/100th of 1%, or 0.01%. If a stock trades at $100 and the spread is $0.02, the spread is:

($0.02 / $100) × 10,000 = 2 basis points

A 2-basis-point spread is tight and typical for a highly liquid large-cap stock. Illiquid stocks might have 100-basis-point spreads or wider, representing $1 spread on a $100 stock. Over hundreds of trades, this compounds into significant drag on returns.

Why Spreads Vary Across Securities​

Large-cap stocks—Microsoft, Apple, Amazon—trade with spreads of just 1-2 cents, or 1-2 basis points, because hundreds of market makers compete to provide liquidity. The intense competition forces spreads tight. Institutional investors trade millions of shares daily in these stocks, making the business of market making highly profitable even on small spreads.

Mid-cap stocks trade with slightly wider spreads, perhaps 3-5 cents. Smaller-cap stocks trade with wider spreads still—sometimes 10-50 cents or more. Penny stocks and illiquid microcaps might trade with spreads of dollars or more. The correlation is clear: the larger, more liquid, and more heavily traded the security, the tighter the spread.

This matters for your portfolio composition. If you exclusively trade in highly liquid large-cap stocks, spreads cost you very little. If you trade smaller companies or less common securities, spreads become a significant drag on returns. Many retail investors unconsciously pay much larger spreads than they realize because they trade less-liquid securities without thinking about it.

Spreads Across the Trading Day​

Spreads are tightest during the middle of the regular trading day (roughly 10:30 AM to 3:30 PM ET) when market activity peaks. At the open (9:30 AM ET), spreads widen because many orders are being placed simultaneously and uncertainty is high. As the market settles, spreads tighten. Near the close (3:30 PM to 4:00 PM ET), spreads sometimes widen again as traders exit positions before the overnight close.

Before regular hours (pre-market: 4:00 AM to 9:30 AM ET) and after regular hours (after-hours: 4:00 PM to 8:00 PM ET), spreads are much wider because fewer market makers are active and fewer traders are participating. If you absolutely must trade during extended hours, expect to pay wider spreads than during regular trading hours.

Spreads During Market Stress​

When volatility spikes, spreads widen dramatically. During earnings announcements, Fed decisions, or geopolitical crises, the order book becomes chaotic. Market makers, facing increased risk of adverse price moves, widen their spreads to demand higher compensation. A stock that normally trades with a 1-cent spread might suddenly show a 50-cent spread during a crisis.

During the March 2020 COVID market crash, spreads on high-quality stocks widened 10-fold or more. Even major stocks saw spreads widen from 1 cent to 10 cents. For traders trying to sell during the panic, this meant receiving far worse prices. Institutional investors who tried to exit large positions found spreads so wide that they could barely move without moving the price against themselves. For investor guidance on market volatility, see investor.gov.

This is a critical risk management lesson: in stressed markets, liquidity disappears fast, and the cost of trading explodes. Wise traders keep some reserves of cash or holdings, giving them options if markets become dislocated.

Market Maker Inventory and Spread Dynamics​

Market makers adjust spreads based on their current inventory of a stock. If a market maker has accumulated a large long position (too many shares owned), they widen the ask (raise their sell price) to discourage buyers and encourage sellers, hoping to reduce their inventory. If they're short (too many shares owed), they widen the bid to encourage buyers and discourage sellers.

This dynamic creates a feedback loop. If spreads widen because a market maker is trying to reduce inventory, other market makers may interpret the wider spread as a sign of lower demand or higher risk, and they may widen their own spreads. This can cause spreads to overshoot actual changes in fundamental risk.

Sophisticated traders watch market maker behavior and inventory changes. Some proprietary trading firms employ "market impact" algorithms that estimate what price concessions they need to offer to move large quantities through the market without pushing spreads wider.

Bid-Ask Spread vs. Other Trading Costs​

The spread is just one component of trading cost. Other costs include commissions (though these have largely fallen to zero for retail traders at major brokers), exchange fees, regulatory fees, and the cost of unfavorable execution if you use limit orders. Some brokers also profit by paying themselves the spread internally or routing orders to market makers who pay them rebates.

When you sum all trading costs—spread, fees, and execution quality—a seemingly low-cost broker might actually be more expensive than a higher-cost competitor if execution is better. This is why sophisticated institutional traders benchmark their execution costs carefully.

Spread Arbitrage and Statistical Arbitrage​

Certain traders, particularly high-frequency traders, profit by exploiting minute discrepancies in spreads across different exchanges or securities. If Apple trades at a $175.50-$175.52 spread on NASDAQ but a $175.51-$175.51 spread on a different venue, an arbitrageur could buy at $175.51 on one venue and sell at $175.52 on another, capturing a one-cent risk-free profit.

Statistical arbitrage involves identifying securities that trade with unusually wide spreads (suggesting overpriced liquidity costs) and using algorithms to trade them efficiently and reduce spreads over time. These strategies are complex and require substantial capital and technology, but they can extract significant value from spread inefficiencies.

Retail traders cannot compete with this kind of arbitrage, but understanding that it exists helps you appreciate why market spreads tend to be relatively efficient. If spreads became wildly inefficient, arbitrageurs would step in and correct them.

Strategies to Minimize Spread Impact​

Use limit orders instead of market orders. If you place a limit order to buy at a price between the bid and ask, you might get a better price than the ask, or you might not fill at all. The tradeoff is reduced certainty of execution but potentially lower cost. For patient traders, this often pays off.

Trade during peak liquidity hours. By concentrating your trading during mid-day hours when spreads are tightest, you can reduce spread costs automatically. Avoid opening and closing positions during the first and last hours of the trading day unless necessary.

Avoid trading illiquid securities. If you need to trade penny stocks or micro-cap companies, accept that spreads will be wide. Alternatively, allocate your money to more liquid securities where you can trade efficiently.

Break large orders into smaller pieces. Instead of submitting a 10,000-share market order at once (which will consume all available offers at the best ask and push into worse prices), submit smaller orders throughout the day. This gives you a better average execution.

Use algorithmic execution. Institutional investors and some sophisticated retail traders use execution algorithms that break orders into pieces and execute across time, aiming to minimize market impact. Some brokers offer this to retail clients.

Real-world examples​

When you buy 100 shares of Apple at market during regular hours, you might pay an ask of $175.52 when the bid is $175.51—a one-cent spread. Your spread cost is 100 × $0.01 = $1. This seems negligible. But if you do this 50 times a month (typical for active traders), you're paying $50 per month in spread costs, or $600 per year, purely for the convenience of immediate execution.

Suppose instead you trade a micro-cap biotech stock. The bid is $12.00 and the ask is $12.50—a 50-cent spread, or 4,167 basis points. Buying 1,000 shares at market costs you $500 in spread cost alone—not including commissions or other fees. If you wanted to exit the same position the next day, you'd face another $500 spread cost round-trip. This means you need the stock to move up more than 4% just to break even on spread costs.

A professional market maker at Virtu or Citadel might profit by posting tight spreads on major stocks. They might buy 100,000 shares of Apple at the bid of $175.51 and sell 100,000 shares at the ask of $175.52 on a single day, capturing 100,000 × $0.01 = $1,000 in spread profit. Repeated thousands of times per day, this becomes a profitable business.

During the March 2020 COVID market crash, spreads on even major stocks widened dramatically. A stock that normally traded with a 1-cent spread might show a $0.50 spread. Retail investors trying to sell during the panic found they received prices 50 cents worse than what they thought was the bid. Some traders who had limit orders to sell at the old prices couldn't execute at all because no buyers existed at any price.

Common mistakes​

Mistake 1: Ignoring spread cost in backtests. Many retail traders backtest trading strategies without including spread costs. This makes the strategy appear far more profitable than it actually is in live trading. A strategy that shows 8% annual returns before costs might show only 3-4% after accounting for spreads.

Mistake 2: Trading illiquid securities casually. Retail traders often focus on finding the "next big stock" without considering liquidity. Even if you find a cheap micro-cap stock, the 2-3% spread cost on every trade makes profiting very difficult.

Mistake 3: Using market orders thoughtlessly. Many retail traders submit market orders out of habit, paying the spread cost unnecessarily. For illiquid securities, using limit orders and waiting for better fills could save significant money.

Mistake 4: Not understanding timing cost. Even if you execute perfectly, buying in the morning and selling in the afternoon might cost you more due to spread widening during volatile times. Some traders systematically hold overnight to avoid daytime volatility spikes.

Mistake 5: Underestimating cumulative spread impact. A trader who pays 10 basis points on 100 trades per year might think that's trivial—roughly 100 basis points total. But if investment returns are 8% per year, losing 1% to spreads reduces net returns by 12.5%. Over decades, this compounds into massive wealth destruction.

FAQ​

What's a typical bid-ask spread for common stocks? For highly liquid stocks like Apple, Microsoft, or Tesla, spreads are typically 1-2 cents, or 1-2 basis points. For medium-cap stocks, spreads might be 5-10 cents. For small-cap stocks, spreads can be 25-50 cents or wider. Penny stocks often trade with dollar spreads or more.

Can I negotiate a better price than the ask? Not with a market order—you'll pay the ask. With a limit order, you can post whatever price you want, but you might not fill. Some institutions negotiate directly with large sell orders ("block trades"), but this is not available to retail traders.

Do electronic communication networks reduce spreads? Yes. Competition between venues (NASDAQ, NYSE, various electronic communication networks) generally tightens spreads because market makers can pick the venue with the best opportunity. However, a fractional-cent improvement in spread might be offset by slightly worse execution quality or higher fees on some venues.

Why don't market makers post even tighter spreads? Posting tighter spreads increases risk per trade (lower profit margin) without necessarily increasing volume proportionally. Market makers optimize their risk-return tradeoff. If they posted spreads so tight that they barely made money, they'd have less capital to invest in technology and market making, ultimately hurting the market.

What's the spread on options and futures? Spreads in options and futures vary by contract liquidity. Deep, liquid contracts like ES (E-mini S&P 500 futures) might trade with $0.25 spreads (equivalent to about 0.25 basis points). Far out-of-the-money options in illiquid stocks might trade with 20-30% spreads—absolutely enormous.

How do I see the real spread during extended hours? You can see bid-ask quotes during pre-market and after-hours on most brokers, but the spreads will be visibly wider—often 2-10 times wider than during regular hours. This is because fewer market makers are active and liquidity is lower.

Do discount brokers have worse execution than full-service brokers? Not necessarily. Many discount brokers (Fidelity, Schwab, Interactive Brokers) offer excellent execution and tight spreads through direct market access. Some execute against their own dealers, which can have advantages or disadvantages depending on market conditions. For information on broker regulation, see sec.gov and nasdaq.com.

Summary​

The bid-ask spread is the difference between the highest price buyers will pay and the lowest price sellers will accept. It represents the direct cost of immediate execution—every time you submit a market order, you pay the spread. Spreads are tightest (1-2 basis points) in large, liquid stocks and widen dramatically (100+ basis points) in illiquid securities. Spreads widen during market stress and volatility, tighten during peak trading hours, and vary significantly across securities. Market makers profit from spreads, capturing the difference between what they pay and what they collect. Understanding spread costs and strategically minimizing them—through limit orders, peak-hours trading, and choosing liquid securities—can meaningfully improve long-term trading returns.

Next​

Read next: Market Depth, Explained — learn what the full order book depth tells you about liquidity and price levels.