Short answer: the bid ask spread is the gap between the highest price a buyer is currently willing to pay and the lowest price a seller is currently willing to accept. You buy at the ask and sell at the bid, so the spread is a cost you pay the moment you enter a position. Narrow spreads signal deep, active markets. Wide spreads signal thin ones.
The two prices behind every quote
Open any order book and you see two live numbers. The bid is the best available buy order. The ask, sometimes called the offer, is the best available sell order. Between them sits the spread, and no trade happens there unless someone crosses it.
That asymmetry has a practical consequence. A position is underwater the instant it opens, by exactly the width of the spread. On a liquid instrument that cost is trivial. On a thin one it can exceed the profit target of a short-term trade.
Exchanges publish the rules that govern how those quotes form and how orders interact with them. The NYSE trading information pages describe the auction and continuous trading mechanics that set the reference prices most other venues follow.
Calculating the spread and what it costs you
The absolute spread is simple subtraction:
Spread = ask price minus bid price
Comparing across instruments needs the relative version, which expresses the gap as a percentage:
Relative spread = (ask minus bid) divided by the midpoint, times 100
Worked example. An instrument quotes 100.00 bid and 100.10 ask. The absolute spread is 0.10. The midpoint is 100.05, so the relative spread is roughly 0.10 percent. If you buy and sell one lot immediately, you lose 0.10 per unit before commissions.
Now scale that. A trader taking twenty round turns a day on that instrument pays the spread forty times. Even at a tenth of a percent per crossing, the annual total dwarfs most subscription and platform fees. This is why active traders study spreads with more care than they study indicators.
| Market type | Typical spread character | Practical effect |
|---|---|---|
| Major currency pairs | Very narrow | Scalping remains viable |
| Large index products | Narrow | Costs stay low intraday |
| Major cryptocurrencies | Narrow in size, wider in stress | Watch weekend and news conditions |
| Small or illiquid instruments | Wide and unstable | Short holding periods rarely pay |
| Any market during news | Temporarily much wider | Slippage risk rises sharply |
What makes spreads widen and narrow
Four forces do most of the work.
- Liquidity. More resting orders at more price levels means a smaller gap between the best bid and best ask. Thin books widen naturally.
- Volatility. When prices move fast, market makers widen quotes to protect themselves from being picked off. Spreads and volatility rise together.
- Time of session. Overlapping sessions concentrate participants. Spreads are usually tightest when the main sessions for an instrument are open, and widest in the quiet hours.
- Scheduled events. Around major releases, quotes widen before the number and stay wide until the market settles. Central bank calendars such as the Federal Reserve FOMC schedule tell you in advance which sessions carry that risk.
Instrument structure matters too. Some products quote fixed spreads that stay constant but sit wider on average. Others quote variable spreads that are tighter most of the time and widen sharply under stress. Neither is universally better, and the right choice depends on when you actually trade.
Strategies for reducing what the spread costs you
- Trade liquid instruments. The simplest and largest improvement available to most traders.
- Use limit orders where you can. A limit order joins the book instead of crossing it, so you avoid paying the spread on entry. The tradeoff is that you may not get filled.
- Avoid the thinnest hours. Spreads widen when participation drops, which is often exactly when nothing is happening anyway.
- Step aside around scheduled releases. Entering seconds before a major number means paying a wide spread and accepting slippage on the stop.
- Match holding period to cost. If the spread is a meaningful share of your average target, the strategy is not viable on that instrument.
- Measure it. Log the spread at the moment of entry for a month. Most traders are surprised by the total.
Spread is only one component of trading cost. Commissions, financing on leveraged positions, and slippage on stops all add to it. the SEC's investor guidance on margin explains how the financing side works when positions are held with borrowed funds, and those charges accrue whether or not the trade works.
Risks and limitations of reading spreads
The spread is a snapshot of the top of the book. It says nothing about how much size sits at those prices. An instrument can show an attractive one tick spread with almost no volume behind it, and a large order will then walk through several levels at progressively worse prices. That difference between the quoted spread and the price you actually receive is slippage, and it is often the larger cost.
Displayed spreads can also mislead during fast markets. Quotes update faster than most retail screens refresh, so the number you see may already be stale when you click. Treat the quoted spread as an estimate of cost rather than a guarantee.
Finally, a narrow spread is not a reason to trade. Low cost makes a good strategy cheaper to run. It does nothing for a strategy without an edge.
Where prop firm evaluations fit
Traders working through an evaluation feel spread costs more acutely than most, because a fixed profit target and a fixed daily loss limit leave little room for avoidable friction. Pivex runs its programme on Match-Trader with forex, indices, metals, and major cryptocoins, and the practical lesson is the same across all of them: pick the sessions where your instrument quotes tightest, and let the cheaper conditions do part of the work.
Next step: record the spread on your main instrument at four fixed times over one week, then compare the numbers. You will usually find one or two windows where the same trade costs noticeably less, and shifting your activity into them is free performance. Traders running a Pivex evaluation can do the same audit on Match-Trader, where the tighter sessions on major pairs and indices do part of the work for you. For the practical side of that, see our guide to slippage.
Related guides: market liquidity and the best pairs for scalping.
Before participating, review Pivex's current program rules and decide whether a simulated proprietary trading evaluation fits your experience and risk limits. Participation does not guarantee a reward, income, or any particular trading result.