Direct answer
The spread you see in minor currency pairs is mainly the result of (1) liquidity in the underlying market, (2) short-term volatility, (3) how orders are matched and executed through the broker’s execution venue and systems, and (4) broker policies and cost components that determine what the quote needs to cover.
Mechanics: what “spread” means
A spread is the difference between a quoted bid price (the price a trader can sell at) and an ask price (the price a trader can buy at). In practice, your total trading cost is not only the raw spread: it can also include commissions, financing-related charges, and any operational effects of order execution (for example, whether a quote holds steady or changes while your order is processing).
For minor pairs, the underlying economic reality is the same as for major pairs, but the market depth is often thinner. “Minor pair” typically means currency combinations that do not include the most traded “major” currencies (such as those paired with USD). When fewer participants actively trade a pair, fewer limit orders are resting in the market, which can make the bid/ask gap widen more easily.
Variable factors: liquidity, volatility, and execution venue
Liquidity effects (depth and trading interest). When liquidity is lower, the market can move from “easy matching” to “scarcer counter-orders” more quickly. That increases the compensation required by liquidity providers (or by systems that simulate liquidity) for the risk of holding inventory at an unfavorable price. The result is commonly wider spreads, especially during times when fewer orders are posted.
Volatility effects (speed of price changes). Volatility increases the probability that quotes become outdated quickly. If prices can jump between bid and ask during the time your broker is processing orders, the broker (or any quoting mechanism) may widen the spread to manage adverse selection risk.
Execution venue and order flow effects. Even with the same underlying market, different execution paths can create different observed spreads. For example, a broker may route orders to external venues, internalize some flow, or rely on liquidity aggregation. Each approach has different latency, pricing sources, and reconciliation steps. Those implementation details can change how quickly quotes update and how “tight” the displayed spread can be in fast market moments.
Broker-policy effects: what can change the quote you see
Brokers may apply policies that affect the quoted spread and the effective cost. Examples of policy-like variables (without assuming any one broker’s approach) include:
- Quote management and risk controls. If a broker needs to control inventory exposure or protect against rapid price moves, it may adjust spreads or quote availability.
- Commission vs spread structure. Some providers present costs partly via commission and partly via spread width. If the commission structure changes, the “effective cost” may shift even when the displayed spread looks similar.
- Order handling rules. Execution timing, minimum distance rules, and how the broker handles partial fills can affect what you ultimately pay compared with the initial displayed bid/ask.
- Time-of-day effects. Liquidity often changes across trading sessions. That means spread behavior can be different at the start of a session versus mid-session.
Limitations and failure modes (what can go wrong with your expectations)
- No real-time prediction from history. Past average spreads do not guarantee future costs. Spread widenings can occur quickly if liquidity thins or volatility spikes.
- Displayed spread vs effective cost mismatch. A narrow spread can still come with other costs (commissions, execution slippage during quote changes, or financing-related charges).
- Hidden dependence on execution conditions. Two trades at different sizes or different times can produce different realized costs, even with the same pair.
- Assumptions for any “example.” If you do a back-of-the-envelope estimate (for instance, converting a spread in price terms into an approximate cost in account currency), you must state assumptions such as lot size, conversion rates, and whether the quote is held for the entire execution. Without those assumptions, the calculation is not verifiable.
Verification: how to check what matters for a specific situation
To independently verify which factors dominate, avoid relying on a single snapshot. Instead:
- Compare spreads across multiple times (including quieter and more active periods) to see liquidity and volatility sensitivity.