Bid-Ask Spread Explained: What It Is and Why It Costs You Money

Every time you buy or sell a stock, you pay a cost that doesn't show up as a commission line item. It's called the bid-ask spread, and for active traders, it can easily exceed what you pay in brokerage fees.

For long-term investors, the spread is a minor nuisance. For day traders making dozens of transactions, it's a meaningful drag on returns. Understanding it is one of the foundations of trading cost management — and knowing how to minimize it through order type selection is a skill that pays off immediately.

What Are the Bid Price and Ask Price?

Every stock quote you see has two prices:

• The bid price is the highest price a buyer is currently willing to pay for the stock.
• The ask price (also called the offer) is the lowest price a seller is currently willing to accept.

These two prices are almost never the same. The bid is always lower than the ask. The difference between them is the spread.

A simple example: Apple (AAPL) might show a bid of $213.45 and an ask of $213.47. The spread is $0.02. That's 2 cents per share.

If you place a market order to buy 100 shares, you'll buy at the ask — $213.47 per share. If you immediately turn around and sell those 100 shares with another market order, you'll sell at the bid — $213.45. You've made no directional bet, but you're already down $2.00 (100 shares × $0.02 spread). The market maker captured that $2.00.

Why Does the Bid-Ask Spread Exist?

The spread is how market makers get compensated for providing liquidity.

Market makers are firms (and today, often algorithmic trading firms) that stand ready to buy or sell any stock at any time. They quote a bid price they'll buy at and an ask price they'll sell at — simultaneously — for every moment the market is open. This service is enormously valuable to markets: without market makers, you might place a buy order and wait minutes or hours for a willing seller to appear.

In exchange for this service, market makers profit from the spread. They buy at the bid and sell at the ask, pocketing the difference on thousands of transactions daily. Their goal is not to take directional bets on stocks — it's to maintain balanced inventory and consistently capture the spread.

This means the spread isn't a fee charged to you directly — it's embedded in the execution price. Your broker might charge $0 in commissions, but the spread cost is always there.

How to Calculate the Spread

The spread calculation is straightforward:

Spread = Ask Price − Bid Price

For a percentage cost (more useful for comparing across stocks at different price levels):

Spread % = (Ask − Bid) / Ask × 100

Notice how the dollar spread on the penny stock is smaller than the small-cap, but the percentage cost is catastrophic. A trader paying a 20% spread needs the stock to move 20% just to break even on a round trip. That's not trading — it's an uphill battle against transaction costs.

The spread percentage is the correct way to compare trading costs across stocks at different price levels.

What Determines the Spread Size?

Three factors drive how wide or tight a spread is on any given stock:

1. Trading Volume and Liquidity

This is the dominant factor. High-volume, highly liquid stocks (Apple, Microsoft, SPY, QQQ) have enormous competition among market makers — dozens of firms fighting to capture spread, which drives it down to near-zero in dollar terms. Thinly traded stocks have fewer market makers competing, which allows wider spreads to persist.

Rule of thumb: If a stock trades under 500,000 shares per day, expect spreads to be noticeably wider than mega-cap names. Under 100,000 shares per day, spreads can be significant enough to seriously impact trade economics.

2. Price Volatility

More volatile stocks require market makers to carry more inventory risk. If a stock can move 5% in an hour, a market maker who bought at the bid faces the possibility of the stock declining before they can sell at the ask. To compensate for this risk, they widen the spread. This is why spreads on individual biotech stocks around FDA decision dates can blow out dramatically — the event risk is enormous.

3. Time of Day

Spreads are widest at market open (9:30–9:45 AM ET) and narrowest during peak midday trading hours (roughly 10:30 AM–3:00 PM ET). At the open, uncertainty is high: overnight news is being absorbed, pre-market pricing is being reconciled with full-session liquidity, and institutional orders are hitting simultaneously. Market makers widen spreads to protect themselves in this chaotic environment.

After 3:30 PM ET, spreads often widen again slightly as institutional end-of-day rebalancing flows introduce uncertainty.

For cost-sensitive traders, midday execution tends to produce the tightest spreads.

Typical Spreads by Stock Type

This table gives you a practical reference for what to expect when trading different categories of stocks:

Spread vs. Commission: Which Costs More?

At zero-commission brokers (Robinhood, Webull, Fidelity, Schwab), the spread is often the only explicit per-trade cost. But which is bigger — the spread or what you'd pay in commissions at a full-service broker?

For highly liquid large-cap stocks, the answer used to be "about the same" when full-service commissions were $5–$10 per trade. At zero commissions, the spread is now the dominant cost for short-term traders.

Example: Trading 100 shares of AAPL at a $0.02 spread costs $2.00 in spread drag on a round trip. A traditional $5 commission per side would cost $10.00. Zero commission wins — but the spread still isn't free.

For a day trader making 20 round trips per day in a $50 stock with a $0.05 spread:

• Spread cost: 20 × 100 shares × $0.05 × 2 (round trip) = $200/day
• Commission cost at $0: $0
• Total: $200/day in spread cost alone, before any market moves

This is why spread awareness matters far more to frequent traders than to investors who hold positions for months.

Limit Orders: How to Avoid Paying the Full Spread

The most powerful tool for reducing spread cost is the limit order.

A market order executes immediately at the best available price — which means you buy at the ask (the higher price) and sell at the bid (the lower price). You're always on the wrong side of the spread.

A limit order specifies the maximum price you'll pay (when buying) or minimum price you'll accept (when selling). If you place a buy limit order at the bid price or inside the spread, you're essentially becoming the market maker — offering to buy at a price between the bid and ask, and waiting for someone to hit your order.

Example: Stock is bid $50.00 / ask $50.10.

• Market order to buy: executes at $50.10 (you pay the spread)
• Limit order at $50.05: you split the spread — if a seller accepts, you pay $0.05 less than the ask
• Limit order at $50.00 (at the bid): you pay nothing above the bid, but may not fill immediately

The trade-off: limit orders introduce execution uncertainty. If the stock moves away from your limit price before your order fills, you miss the trade. Market orders guarantee execution but not price; limit orders guarantee price but not execution.

For investors who aren't in a rush, placing buy limit orders inside the spread or at the bid is a straightforward way to reduce entry costs. For traders who need immediate execution (momentum plays, stop-loss exits), the guarantee of execution from a market order often outweighs the spread cost.

Level 2 Quotes: Seeing the Full Order Book

The standard quote shows only the best bid and best ask. Level 2 quotes (also called the full order book or market depth) show every bid and ask order waiting at every price level below and above the current price.

A Level 2 view looks like this:

This tells you:

• The best bid is $50.00 for 3,200 shares — if you place a market sell order for more than 3,200 shares, the remainder fills at $49.95 or lower
• There is significant buy support at $49.90 (12,000 shares) — this acts as a near-term floor
• The ask side thins at $50.20 — if buyers push, there isn't much resistance above $50.15

Level 2 data is available in most active trading platforms (Webull, Interactive Brokers, Thinkorswim, etc.) and is extremely useful for timing entries and exits in thinly traded names where your order size could meaningfully impact the price.

For most retail investors buying large-cap stocks, Level 1 (standard bid/ask) is sufficient. For anyone trading with position sizes above $25,000–$50,000 in smaller stocks, Level 2 becomes valuable for understanding how your order will actually be filled.

How Spread Affects Day Traders vs. Long-Term Investors

The spread's impact is directly proportional to how frequently you trade.

For a long-term investor holding stocks for months or years, the spread is a one-time cost at entry and exit — an annoyance rather than a meaningful drag. Buying $10,000 of a stock with a 0.05% spread costs $5.00 on entry and $5.00 on exit. Over a two-year holding period, that's essentially noise.

For a swing trader holding positions for days to weeks, spread matters more but remains manageable as long as they stick to liquid, large-cap names. The primary lever is using limit orders for entries rather than market orders — this alone can reduce round-trip costs by 30–50%.

For a day trader entering and exiting positions multiple times per day, the spread is a critical operational cost. Day traders need to ensure:

1. They trade stocks with sufficient daily volume (generally >1 million shares/day for meaningful scale)
2. They use limit orders for entries, accepting the execution risk
3. They size positions large enough that the expected gain per trade significantly exceeds the spread cost
4. They avoid the open (9:30–9:45 AM) for non-momentum plays when spreads are at their widest

A common rule among professional day traders: if the expected profit target for a trade doesn't exceed 3× the round-trip spread cost, the trade isn't worth making.

Spreads in Pre-Market and After-Hours Trading

Everything discussed above applies to regular market hours. In pre-market (4:00 AM – 9:30 AM ET) and after-hours (4:00 PM – 8:00 PM ET) sessions, spreads are dramatically wider due to lower liquidity.

A stock with a $0.02 regular-session spread might show a $0.50–$2.00 spread in after-hours trading. This is why limit orders aren't just recommended in extended sessions — they're mandatory at most brokers.

This also explains why after-hours earnings moves should be monitored but not necessarily acted on immediately. The wide spreads mean you're paying a significant premium for the urgency of trading outside regular hours. If the move is large enough and your conviction is high, the cost can be worth it. For smaller moves, waiting for the regular-session open often produces better execution.

Stock Alarm Pro's real-time quote data shows you current bid/ask prices on any ticker across all sessions — and alerts fire the instant a stock reaches your target price so you can place your limit order at exactly the right moment, whether that's at 4:30 PM during after-hours or at 9:45 AM once the open-hour volatility settles. Set up a price alert →

Practical Takeaways

For every trade, check the spread before entering:

• Spread below 0.1%: use market or limit orders freely
• Spread 0.1–0.5%: use limit orders, consider whether the target gain justifies the cost
• Spread above 0.5%: be very deliberate; the position needs a larger expected move to be profitable

Use limit orders by default:

• For non-urgent entries in liquid stocks, split the spread or bid at the inside. It takes discipline but meaningfully reduces entry cost over time.
• For exits where urgency matters, market orders are appropriate. Don't penny-pinch on exits when your thesis has changed.

Avoid thinly traded stocks unless you have conviction:

• A 2% spread on a $10 stock means you need a $0.20 move just to break even on entry. That's not a small hurdle.

Use the screener to check average volume on any stock you're considering — volume is the single best proxy for spread tightness. Filtering for stocks with daily volume above 500,000 shares dramatically reduces the universe of illiquid, wide-spread names.

Conclusion

The bid-ask spread is one of those concepts that seems simple on the surface — just the difference between two prices — but has real consequences for trading profitability when you add it up across dozens or hundreds of transactions.

The core lessons are: spreads exist because market makers need compensation for providing liquidity; they're widest for illiquid, volatile, and small stocks; they're highest at market open and in extended-hours sessions; and the single most effective tool to reduce your spread cost is the limit order.

Understanding how the spread works puts you ahead of most retail traders, who place market orders without a second thought and consistently give up the spread on every single trade.

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