Bid-Ask Spread Explained: What It Is and What It Costs You
Updated August 2026
The bid-ask spread rarely shows up as a line on a statement, yet it is paid on every single trade. It is built directly into the price itself: buy at the ask, sell at the bid, and the gap between those two numbers is gone before the position has moved a cent.
This guide breaks down what the spread is, how to calculate it, what makes it widen or narrow, and why it functions as a real cost even without a visible fee attached. It also covers how the spread applies when you trade stock CFDs on Ouinex, and a few practical ways to keep its cost down.
What Is the Bid-Ask Spread?
The bid-ask spread is the difference between the highest price a buyer is willing to pay (the bid) and the lowest price a seller is willing to accept (the ask) for an asset.
At any given moment, a market quotes two prices, not one. The bid is the best price currently on offer from buyers. The ask, sometimes called the offer, is the best price currently on offer from sellers.
A market maker, also called a liquidity provider, quotes both prices and stands ready to trade at them, earning the difference between the two on every trade it fills. The U.S. Securities and Exchange Commission defines the spread as a transaction cost investors pay in addition to any commissions or mark-ups, and that framing matters: the spread is a cost regardless of what a broker charges on top of it.
Ouinex covers the concept in brief in Ouinex Talks: Spreads. This guide goes further into the calculation, the drivers behind it, and how to manage its cost.
Both the bid and the ask move constantly as new buy and sell interest enters the market, so the spread itself is dynamic. A $0.05 spread on a stock right now might be $0.03 an hour later, or $0.15 during a volatile stretch, on the exact same instrument.
How to Calculate the Bid-Ask Spread
The formula is simple:
Spread = Ask Price - Bid Price
Worked example: say a stock is quoted with a bid of $100.00 and an ask of $100.05. The spread is $100.05 minus $100.00, or $0.05.
On a lower-priced or more liquid instrument, that same $0.05 can represent a much larger relative cost, which is why the spread is often expressed as a percentage of price rather than as a raw number. A $0.05 spread on a $100 stock is a small relative cost. The same $0.05 spread on a $5 stock is a full percentage point, even though the dollar figure is identical.
What Determines the Size of a Spread?
Four factors consistently drive how wide or narrow a spread is.
Liquidity: more liquid markets, those with a high volume of active buyers and sellers, typically have tighter spreads. Competition between participants narrows the gap between the best bid and best ask. Thinly traded assets carry wider spreads because fewer competing quotes leave more room between the two.
Volatility: spreads widen during volatile or fast-moving conditions. Market makers widen their own quotes to account for the risk of prices moving against them before they can offset a position.
Market hours: spreads can widen outside peak trading hours or around major news events, when fewer participants are actively quoting prices and liquidity thins out. A stock that trades with a tight spread during its most active hours can show a noticeably wider one overnight or around a scheduled earnings release.
Order size and market impact: larger orders can widen the effective spread a trader pays. A quoted spread reflects the best available price for a limited number of shares. An order large enough to exhaust that quote has to reach deeper into the order book, filling at progressively worse prices, a cost known as market impact or slippage.
These factors compound. A thinly traded stock during a low-liquidity overnight session, hit by unexpected volatility, can see its spread widen far more than any single factor explains on its own.
The Bid-Ask Spread as a Trading Cost
The bid-ask spread is an implicit transaction cost paid on every trade, separate from any explicit fee. Buying at the ask and immediately selling at the bid gives up the full spread before any commission or funding cost applies.
This matters more for frequent or short-term traders. A single trade barely registers the spread against a larger price move. A trader making dozens of trades a day pays that cost repeatedly, and it compounds into a real drag on returns, often more than the visible fees a trader is more likely to track.
Here is the part most trading education skips: the spread is invisible in a way a commission line item is not, and that invisibility is part of why it gets underweighted. European regulators require CFD providers to disclose that a large majority of retail accounts lose money, and implicit costs like the spread are a structural contributor to that gap. A trader who never sees a bill for the spread has no natural prompt to account for it, unlike a fee that shows up on a statement. Treating the spread as a real, trackable cost, not just background noise, is one of the more overlooked edges available to a retail trader.
The spread is a real cost on every trade, and its impact is magnified on a leveraged position. Factor it into your entry and exit planning, not just the fee schedule. For a broader look at how Ouinex's costs compare across markets, see Ouinex's cost structure across markets.
How to Reduce the Impact of the Spread
Trade more liquid assets where spreads are naturally tighter. Major, actively traded instruments generally carry tighter spreads than thinly traded ones, simply because more competing buy and sell interest exists at any moment. Sticking to liquid instruments when the strategy allows is one of the simplest ways to cut spread cost without changing anything else about execution.
Watch for predictable spread-widening windows. Spreads tend to widen around market open and close, and around major scheduled news releases, as liquidity providers adjust their quotes for the added uncertainty. Waiting a few minutes after a major release, once the initial volatility settles, often means trading at a meaningfully tighter spread.
Use a limit order instead of a market order when the spread looks unusually wide. A market order accepts the current spread as is. A limit order lets a trader set a price inside the spread and wait for it to be met, at the cost of the order possibly not filling at all. Ouinex's market order vs limit order guide covers that trade-off in more depth.
FAQ: Bid-Ask Spread Questions Answered
What's the difference between the bid price and the ask price?
The bid price is the highest price currently offered by buyers. The ask price is the lowest price currently offered by sellers. A trader selling into the market fills at the bid; a trader buying from the market fills at the ask. Buying and immediately selling the same asset at the same moment results in a small loss equal to the spread, even with no price movement at all.
Why is the spread wider for some assets than others?
Spreads are driven mainly by liquidity and volatility. Highly liquid, actively traded assets tend to have tighter spreads because more buyers and sellers compete to trade at any moment. Thinly traded or highly volatile assets carry wider spreads because fewer participants are quoting and the risk to those who do is higher. Major currency pairs and large-cap stocks sit at the tighter end; smaller-cap stocks and less common instruments sit at the wider end.
Does the spread change during volatile markets?
Yes. Spreads typically widen during volatile conditions as market makers adjust their quotes for the increased risk of price moving against them before they can offset a trade. A trade that looked reasonably priced in calm conditions can become noticeably more expensive to enter once volatility picks up, even before the underlying asset has moved much.
How does the bid-ask spread affect crypto trading?
The same principles apply to crypto as to any other asset class: more liquid pairs tend to have tighter spreads, less liquid ones carry wider spreads. Because crypto markets can spike sharply, spreads on less liquid crypto pairs can widen more dramatically and more quickly than spreads on established markets like major forex pairs.
Does the spread work the same way on a stock CFD as it does on the underlying stock?
The mechanics are the same: a CFD quote also has a bid and an ask, and the gap between them is a cost paid on entry and exit. Trading a stock CFD on Ouinex means speculating on the price of the stock through the derivative, not owning the underlying share, but the spread cost behaves identically to how it behaves in the cash market. It still widens with volatility, thins with liquidity, and applies on both sides of the trade.
Conclusion
The bid-ask spread is not a fee you will find on an invoice, but it is real money, paid on the entry, paid again on the exit, and quietly present on every trade regardless of asset class. The mechanics are simple: spread equals ask minus bid, liquidity and volatility drive its size, and larger orders can widen the effective cost further. What separates traders who manage it well is treating it as a planned cost rather than a background detail, especially on leveraged positions where its impact compounds. If you are ready to see how spread and execution work in practice, you can explore Ouinex's stock CFD markets across a range of major names.
Sources
CFD trading involves leverage and can result in losses that exceed your initial deposit. You may lose the full amount you invest, and your investment does not benefit from any form of financial protection. Past performance is not a reliable indicator of future results.
