At noon on Monday, Sam closed the study layout from Lesson 33: RSI, MACD and Bollinger Bands and looked at the line in his notebook that had ruled ABCD out from the start: "12-cent spread."

He'd done the math once already, in Lesson 25: the spread alone on a full-size ABCD position would cost more than his whole risk budget. But one trade is easy to shrug off. What about a week of practice trades? A month?

This lesson answers that with arithmetic, then wraps up everything Module 3 has taught about reading the market.

In 30 seconds

  • The Bid-Ask SpreadThe bid-ask spread is the difference between the highest price buyers will pay and the lowest price sellers will accept — it's an immediate, invisible transaction cost on every trade you make.Read definition → is the difference between the best price buyers are bidding and the best price sellers are offering; it's the cost of trading immediately.
  • If you buy at the offer and sell at the BidThe bid is the highest price a buyer is currently willing to pay. When you sell with a market order, you receive the bid price.Read definition →, you pay the full spread on every round trip, even if the price never moves.
  • Spread cost equals spread times shares, every round trip. Small spreads add up with size and frequency, and a wide spread also raises the Win RateWin rate is the percentage of your trades that result in a profit — calculated as (number of winning trades ÷ total trades) × 100 — and while commonly cited as a measure of trading success, it means very little without also knowing the averRead definition → you need just to break even.
  • Spreads are usually tightest in liquid stocks during regular hours and widest in thin stocks, around news and outside regular hours.

In this lesson you'll learn what the spread is, why it exists, how to calculate what it costs you, what makes it wider or tighter and how to keep it small. It ends with a recap of Module 3. If you're new, start with Lesson 25: Liquidity and Volume, where the spread first appears as a sign of LiquidityLiquidity in trading refers to how easily you can enter and exit a position at a fair price — a liquid stock has high volume and a tight bid-ask spread, allowing large orders to be filled quickly without moving the price, while an illiquid Read definition →.

What is the bid-ask spread?

The bid-ask spread is the difference between the highest price someone is currently bidding to buy a stock and the lowest price someone is currently offering to sell it. If XYZ is bid at $53.80 and offered at $53.82, the spread is 2 cents.

The airport currency booth is the classic picture. It buys your dollars at one rate and sells them at a slightly worse one, and both rates sit on the same board. If you swapped money there and swapped straight back, you'd lose the difference without the exchange rate changing at all.

Stocks work the same way. A Market OrderA market order is an instruction to buy or sell immediately at the best available price — it guarantees execution but not the price, meaning in fast or illiquid markets you can receive a significantly worse fill than the last quoted price.Read definition → to buy usually fills at the offer, and a market order to sell usually fills at the bid. That's why a position often shows a small loss the moment you buy: your platform values it at the bid, the price you could sell at right now.

Hypothetical quote: the spread is the ask minus the bid, here 5 cents. Market buys usually pay the ask; market sells usually receive the bid.

Why does the spread exist?

The spread exists because someone has to be willing to trade with you right now, and that willingness has a price. Economist Harold Demsetz described the spread as the price of immediacy: what you pay for not having to wait for a buyer or seller to show up. His study of NYSE stocks found spreads were narrower in stocks that traded more often (Demsetz, 1968).

Market makers and other liquidity providers post both a bid and an offer, earning the difference when they trade both sides and taking the risk that price moves against them in between. Lesson 45: Market Makers and Order Flow covers who they are and how your order reaches them.

The spread isn't a hidden fee from your broker. It's a market cost, and it's there whether your broker charges commissions or not. Lesson 16: Brokerage Costs shows where it sits on the full fee menu.

How do you calculate what the spread costs you?

You calculate spread cost by multiplying the spread by the number of shares, once per round trip. For comparing stocks at different prices, divide the spread by the share price to get a percentage.

Bid / offer
XYZ
$53.80 / $53.82
ABCD (Lesson 25 quote)
$3.40 / $3.52
Spread
XYZ
$0.02
ABCD (Lesson 25 quote)
$0.12
Spread as a share of price
XYZ
about 0.04%
ABCD (Lesson 25 quote)
about 3.5%
Shares for a $4,160 position
XYZ
80
ABCD (Lesson 25 quote)
about 1,200
Spread cost per round trip
XYZ
$1.60
ABCD (Lesson 25 quote)
$144

Hypothetical quotes. Both positions are worth about the same, so the comparison is fair.

The percentage view is what matters for a trade idea. In ABCD, price has to move about 3.5% your way just to get back to even. In XYZ, it has to move a few hundredths of a percent.

Hypothetical: 250 shares at a 4-cent spread costs $10 per round trip, so five trades cost $50 before any commission.

Very short charts show the spread in another way. When trades alternate between the bid and the offer, the last price bounces back and forth even if nothing changed (Roll, 1984). On a thin stock's 1-minute chart, some of the "movement" is simply the spread.

How does the spread change the win rate you need?

A wider spread raises the share of trades you must win just to break even. Picture a trade with a 40-cent stop and a 40-cent target, both measured from the middle of the spread. Buying at the offer and selling at the bid shaves the spread off every win and adds it to every loss.

Spread
$0.01
Net win
$0.39
Net loss
$0.41
Win rate needed to break even
51.3%
Spread
$0.02
Net win
$0.38
Net loss
$0.42
Win rate needed to break even
52.5%
Spread
$0.05
Net win
$0.35
Net loss
$0.45
Win rate needed to break even
56.3%
Spread
$0.12
Net win
$0.28
Net loss
$0.52
Win rate needed to break even
65.0%

DayTradingToolkit calculation: break-even win rate = (0.40 + spread) / 0.80. Per share, before commissions, fees and slippage.

The same trade idea needs to work 52.5% of the time with a 2-cent spread and 65% of the time with a 12-cent spread. Nothing about the chart changed; only the cost of getting in and out did.

The spread is the first trade you lose, every time.

What makes a spread wide or tight?

Spreads are tightest when many traders compete on both sides and widest when few do, or when the risk of trading suddenly rises.

Spreads tend to be tighter
Heavily traded, liquid stocks
Spreads tend to be wider
Thinly traded stocks
Spreads tend to be tighter
Calm, regular-session trading
Spreads tend to be wider
Around news, earnings and halts
Spreads tend to be tighter
Mid-session
Spreads tend to be wider
Near the open and the close
Spreads tend to be tighter
Regular hours
Spreads tend to be wider
Pre-market and after-hours

Time of day matters more than beginners expect. A classic study of NYSE stocks found spreads were wider at the start and end of the trading day than in the middle (McInish and Wood, 1992), and the SEC warns that extended-hours sessions usually have less trading interest and wider spreads (Investor.gov).

There's also a floor. For stocks priced at $1 or more, the minimum quoting increment is currently one cent. The SEC adopted a half-penny increment for the most tightly quoted stocks (SEC), but in June 2026 extended relief from compliance until the first business day of November 2027 and asked staff to review the rule (SEC). For now, a 1-cent spread is as tight as most stocks get.

How can you keep spread costs low?

You keep spread costs low mostly by choosing where and when you trade, and a little by how you place orders.

  • Trade liquid stocks. The single biggest lever. A 1 or 2-cent spread on a busy stock costs a fraction of a 10-cent spread on a quiet one.
  • Check the spread before every trade. It takes a second, and it can change from minute to minute. Lesson 30: Level 2 and Time & Sales shows where to look.
  • Avoid thin hours. Pre-market, after-hours and the first minutes after the open usually cost more to trade.
  • Consider a limit order when the spread is wide. A limit order lets you set your price, even inside the spread, but it isn't guaranteed to execute (Investor.gov). Lesson 43: Order Types explains the trade-off.
  • Trade less often. Every round trip pays the spread again.

The spread is the cost you can see in advance. Slippage, the extra cost when your order fills worse than the quote you saw, comes on top and has its own lesson: Lesson 44: Slippage.

Sam prices a week of practice (hypothetical)

Sam plans to practice one trade a day once his paper routine starts, five a week, at the $4,160 position size from Lesson 3 and the $60 risk limit he's used since.

Hypothetical: one week of spread costs, XYZ vs ABCD

XYZ: 80 shares x $0.02 spread, per round trip$1.60
times Round trips per week5
equals XYZ spread cost per week$8
equals ABCD: 1,200 shares x $0.12, five round trips$720 a week, 90 times as much

Per trade, XYZ's spread is about 2.7% of his $60 risk. ABCD's, $144, is 2.4 times that risk on every single trade. Over a four-week month the gap is $32 against $2,880, almost half of his $6,000 tuition money spent on spreads alone, before a single losing trade.

He adds one line to the rules on his laptop screen: "Check the spread before the chart. If it costs more than 10% of my risk, there's no trade to plan."

Thinking zero commission means free

You're doing it if
You pick a stock because your broker charges $0 to trade it and never look at the bid and offer before clicking buy.
The fix
Before every trade, multiply the current spread by your share count. That's the minimum this round trip will cost, whatever your broker charges.

Your turn: price the spread on two stocks

Spread practice (10 minutes, no orders)

0 of 5 done

Module 3 recap: reading the market

Module 3 taught Sam, and you, to read a chart before trusting it. In one place:

  • Candles and levels. Read finished candles, mark daily levels first, and treat patterns as possibilities with real failure rates (Lessons 21 to 23).
  • Fewer indicators. Volume and one or two lines beat a crowded chart (Lesson 24), and RSI, MACD and Bollinger Bands describe the past without scheduling the future (Lesson 33).
  • Liquidity first. Check volume, dollar volume, spread and your size against what's there before any setup (Lesson 25).
  • Timeframes in order. Daily for context, 5-minute for the setup, 1-minute only to time a level, read from the top down (Lessons 26 and 31).
  • Session lines. VWAP is today's volume-weighted average, and moving averages show the drift; both describe, neither predicts (Lessons 27 and 28).
  • Who's trading. Volume bars show participation, and Level 2 and the tape show what people offer versus what actually trades (Lessons 29 and 30).
  • Gaps and costs. Gaps can jump past any stop, and the spread is a cost you pay on every round trip (Lessons 32 and 34).

Check your understanding

Check your understanding

A stock is bid at $20.00 and offered at $20.05. You buy 300 shares at the offer and sell immediately at the bid. Ignoring fees, what did the round trip cost?

Check your understanding

With a 40-cent stop and a 40-cent target, roughly what win rate do you need to break even if the spread is 12 cents?

Check your understanding

Which session usually has the widest spreads?

Check your understanding

Module 3 review: XYZ breaks above a level on a volume bar about a third of the recent average. What's the most sensible reading?

Check your understanding

Module 3 review: in which order should you read your charts before planning a trade?

Key takeaways

  • The spread is the gap between the best bid and the best offer, and it's what you pay for trading immediately.
  • Every round trip at market costs spread times shares; frequency and size multiply it.
  • Wider spreads raise the win rate you need to break even, before any other cost.
  • Liquid stocks in regular hours have the tightest spreads; thin stocks, news and extended hours have the widest.
  • For most stocks the minimum quote increment is still one cent, as the SEC's half-penny rule has been postponed to November 2027.

Frequently asked questions

Why does my position show a loss right after I buy?
Because your platform usually values the position at the bid, the price you could sell at right now, while you bought at the offer. The gap is the spread. If the stock doesn't move, that's the loss you'd lock in by selling immediately.
Do long-term investors need to worry about the spread?
Much less. They pay it once on the way in and once on the way out, and over years it's small next to the price change. Day traders pay it on every round trip, often several times a day, which is why it matters so much more for them.
Is the spread the same thing as slippage?
No. The spread is the gap you can see in the quote before you trade. Slippage is the extra difference when your order fills at a worse price than the quote you saw, for example because the size at the best price ran out. Both add to your cost.
Can I avoid the spread completely?
Not completely. A limit order at the bid when buying, or at the offer when selling, can avoid paying it, but only if someone trades with you there, and many such orders never fill. In practice, choosing liquid stocks with 1 or 2-cent spreads matters more than order tricks.
What's the smallest possible spread?
For most stocks priced at $1 or more, one cent, because that's currently the minimum quoting increment. The SEC has adopted a half-penny increment for the most tightly quoted stocks, but compliance was postponed until the first business day of November 2027 and the rule is under review.

Up next: which stocks should Sam even look at?

Module 3 is done. Sam can read a chart, check liquidity and price a spread. But he's only ever looked at two stocks, XYZ and ABCD, and there are thousands of US-listed stocks moving every morning. How does anyone find the handful worth watching before 9:30? Lesson 35: Stock Scanners opens Module 4 with that question.

Disclaimer

This lesson is for educational purposes only and is not financial advice. Spreads change constantly and can widen sharply in thin stocks, around news and outside regular hours, and limit orders are not guaranteed to execute. Rule details such as tick sizes can change; check current SEC guidance. All Sam examples and numbers are hypothetical. Trading involves the risk of loss, and nothing here guarantees any result. For our complete disclaimer, visit https://daytradingtoolkit.com/disclaimer.

Article Sources

This lesson relies on SEC rules and guidance and peer-reviewed research.