The bid is the price at which you can usually sell to the dealer; the ask is where you can usually buy. The ask–bid difference is the spread, which can vary with liquidity and volatility. A buy…
Understand the mechanism
The bid is the price at which you can usually sell to the dealer; the ask is where you can usually buy. The ask–bid difference is the spread, which can vary with liquidity and volatility. A buy position typically starts marked at a loss equal to that initial spread, even before commissions or slippage. Spreads may widen during rollover, news or thin trading.
Before applying this topic in a live market, write down the information available before the decision. Distinguish a fact confirmed by a platform specification or official source from an interpretation drawn from a chart. If a key data point is missing, treat it as unknown rather than filling it with a convenient estimate.
Worked example or scenario
If EUR/USD bid is 1.09500 and ask 1.09518, the displayed spread is 1.8 pips. A trade needing a two-pip target leaves little room after costs.The numbers and scenarios in this example are educational illustrations. They are not live quotes, account-specific contract terms, backtested guarantees or a suggestion to place this trade. Consider how the outcome changes when costs, a different contract multiplier, or a faster market are introduced.
Common mistakes and limitations
Treating an advertised minimum spread as an average, or testing a strategy on midpoint candles while ignoring execution prices.
Check whether any assumption depends on a fixed spread, a guaranteed fill, a historical relationship remaining stable, or the availability of a financial product in your country. In practice, execution rules and platform legal entities differ. A correct formula using an incorrect contract multiplier can still produce a dangerously wrong position size.
Four-point practical checklist
- 1
Step 1
Identify the exact instrument and contract terms before doing any arithmetic.
- 2
Step 2
State the risk and assumptions in account currency, not only in chart points.
- 3
Step 3
Check current primary-source information and write down what could invalidate the idea.
- 4
Step 4
Record actual bid and ask snapshots at your planned entry time and estimate the total cost in account currency.
Practice assignment
Record actual bid and ask snapshots at your planned entry time and estimate the total cost in account currency.
Complete the task in a journal, spreadsheet or demo account and keep a record of your assumptions. If you are unable to explain the possible loss in your own account currency, do not substitute a larger position for a missing calculation.
Reflect and self-check
Does understanding this lesson guarantee profit?
No. Understanding mechanisms helps evaluate decisions; it cannot predict market movements or remove trading losses.
Can I use this lesson with any broker?
The principles may transfer, but prices, product rules, contract multipliers, protections and country eligibility must be checked for each provider.