Direct answer
The spread you see in an account base currency is affected by the price difference between buy and sell quotes for the underlying instruments, plus how that difference is translated into your account currency and how your orders are executed. In practice, spread widens when liquidity is lower or volatility is higher, and it can also appear different because the provider converts prices, applies dealing policies, and adds costs that are not always visible as a simple “spread” number.
Mechanics: definition and what “account base currency” changes
A spread is the difference between the bid (the price at which you can sell) and the ask (the price at which you can buy). It is easiest to think of spreads in the currency terms of the traded instrument. But you don’t experience them only in that instrument’s native currency: your account uses a base currency, so the platform must express prices, margin, and transaction results relative to that base.
Two mechanical steps matter:
- Underlying market spread: The bid–ask gap for the traded pair or instrument.
- Account-currency translation: If the account base currency differs from the instrument’s quote currency, the provider (or pricing engine) converts the bid and ask into your base currency terms. Any conversion affects the numerical spread you observe.
To keep this explanation concrete, assume a provider quotes an instrument with a bid–ask difference, and then applies conversion rates to express it in your account base currency. Even if the underlying bid–ask gap stays the same in instrument terms, different conversion rates at the moment of quote can change the converted difference, making the displayed spread in account base currency larger or smaller than you might expect.
Variable factors: liquidity, volatility, execution venue, and policy
Several variable factors commonly push the effective bid–ask gap higher or lower:
Liquidity
Liquidity describes how easily and quickly large orders can be matched with counterparties. When liquidity drops (for example, around major news, market open/close transitions, or quiet trading hours), quotes may widen because participants demand compensation for uncertainty and execution risk.
Volatility
Volatility reflects how quickly prices move. When price movement is fast, spreads often widen. Market makers or liquidity providers may increase the bid–ask distance to reduce the chance of being “caught” on adverse price movement between quote updates.
Execution venue and order handling
Even if two providers display similar spreads, execution venue and order handling can change what you effectively receive. For example, different routing approaches, quote update frequency, and how partial fills or re-quotes are handled can influence the realized cost. This is a limitation: the “spread number” is not the only component of transaction cost.
Broker policy and costs
Providers may operate different policies for pricing and cost presentation. Some costs may be embedded in how quotes are generated, while others may be charged separately (for instance, commissions, financing/margin-related charges, or adjustments tied to instruments). Those elements can change the total cost, even when the headline spread looks unchanged in account base currency.
Evidence or example (with explicit assumptions)
Consider an account base currency that differs from the instrument’s quote currency. Assume:
- The underlying instrument bid–ask spread is constant in its own terms.
- Conversion into the account base currency uses rates that can differ between bid and ask because the conversion market has its own bid–ask gap.
Under these assumptions, the converted spread in account base currency can widen even if the underlying instrument spread does not, because the conversion step introduces its own bid–ask components. If the conversion market is illiquid or volatile, that conversion spread can become a meaningful part of the final displayed spread.
This example is deliberately simplified. In real systems, pricing can involve additional steps such as internal markups, latency differences, and quote-stream refresh rates—any of which can affect what you see.
Limitations and risks: what can go wrong in interpretation
- Spread vs total cost: The displayed spread may not include all costs that affect your outcomes (for example, commissions or other charges). Treat spread as one component, not the entire cost. 2. Timing and quote refresh: Spreads can change quickly.