Direct answer
A worked example of spread definition shows how to calculate spread from quoted bid and ask prices, and how that difference can translate into a cost estimate. The key is to state assumptions (prices, trade size, quote convention, and whether you include commissions/fees) and then separate what is stable (the definition) from what varies (liquidity, pricing model, execution, and additional costs).
Mechanism or definition
Spread definition (basic concept). In foreign exchange quotes, two prices are commonly shown:
- Bid: the price at which you can sell (the dealer buys from you).
- Ask (offer): the price at which you can buy (the dealer sells to you).
Spread is the difference between the ask and the bid:
- Spread (in price terms) = Ask − Bid
Important stable vs variable distinction. The arithmetic definition above is stable. What can vary between situations is:
- the exact bid/ask values you observe,
- whether your execution price matches the displayed quote,
- whether there are extra costs (commissions, financing charges, or other fees) that are not part of the raw spread.
Worked numerical example (with every assumption stated)
Below is one self-contained example using simple assumptions so the calculation can be independently checked.
Assumptions (state up front):
- You are looking at a quote where Ask = 1.10510 and Bid = 1.10490.
- The spread definition uses raw price difference: Spread = Ask − Bid.
- You do not include any commission or other fee; this example isolates spread only.
- You will not convert to profit/loss in money; instead, you compute the spread in quote-price units.
Step 1: Calculate spread in price terms
- Spread = 1.10510 − 1.10490 = 0.00020
Step 2: Interpret the result
- A spread of 0.00020 means the ask is 0.00020 higher than the bid for this quote.
Step 3: Show a simple “where it shows up” thought experiment (still definition-focused)
- If you hypothetically buy at the ask (1.10510) and later sell at the bid (say the bid remains aligned with the same mid-price structure), you would need enough favorable price movement to cover the initial ask–bid gap.
This example stays at the definition level. Converting spread into a money cost requires additional assumptions (trade size, contract units, and the quote convention). The limitation section below explains why that step can change the interpretation.
Evidence or example comparison (two spreads, same method)
To illustrate how the definition behaves under different quoted conditions, reuse the same method with new assumed quotes.
Assumptions for Scenario B:
- Ask = 1.10530
- Bid = 1.10520
- No commissions/fees included
Calculation:
- Spread = 1.10530 − 1.10520 = 0.00010
Comparison:
- Scenario A spread (0.00020) is larger than Scenario B spread (0.00010) under the assumed quotes.
This comparison is purely mechanical: it compares two spread values computed from two assumed ask/bid pairs. It does not claim anything about future behavior.
Limitations and risks
- Displayed quotes may not equal execution prices. The definition uses bid/ask values, but real execution can differ due to slippage or latency. Even with the same spread calculation method, the realized cost can be higher.
- Spread is not the only cost. Commissions, financing charges, and other charges can materially affect total trading cost. A “small spread” quote can still be expensive overall if other costs are larger.
- Contract and conversion assumptions can change money impact. If you translate a price spread (like 0.00020) into a currency amount, you must assume contract size and how the quote is converted. Without those assumptions, the worked example cannot predict real monetary outcomes.
- Market conditions shift. Liquidity can narrow or widen the bid–ask gap. A historical relationship between spread and other variables does not guarantee future results.
Verification and next question
To independently verify the worked example, check the arithmetic:
- Spread = Ask − Bid
- For Scenario A: 1.10510 − 1.10490 = 0.00020
A useful next question is: How do you convert a price spread into a money amount given a specific trade size and quote convention? That conversion depends on additional assumptions beyond spread definition itself.