Direct answer
The spread in AUD crosses is not fixed. It typically changes with market liquidity and volatility, how trading is executed, and what costs or rules a provider applies to order routing and execution. Because “spread” is a real-time market outcome, you can only verify it by observing current quotes and your actual execution cost under your own conditions.
Mechanism and definitions
A spread is the difference between the best bid price (what a buyer is willing to pay) and the best ask price (what a seller is willing to accept). For AUD crosses, this bid–ask difference reflects how quickly and cheaply counterparties can trade the two currencies in that cross.
When you look at AUD crosses, several inputs are in play:
- Liquidity: If many participants are ready to trade the AUD leg of the cross (or the relevant counterparties), bids and asks can stay close.
- Order book depth and immediacy: Even with similar liquidity, the ability to absorb market orders without large price jumps matters.
- Volatility: If prices move quickly, market makers and liquidity providers often widen spreads to reduce the risk of being “picked off” (filled at prices that become unfavorable immediately after).
- Execution venue and routing: Orders may interact with different pools of liquidity. Those pools can have different depth, latency, and pricing.
- Provider policy and fee structure: Some providers combine a tighter quoted spread with separate commission, while others embed more cost into the spread. Also, execution rules can affect whether you get the price you expected.
In practice, the “quoted spread” is only one component of total trading cost. Slippage is the difference between your expected price and the actual fill price, often caused by fast markets or limited liquidity.
Evidence or example (with stated assumptions)
Assume you are trading an AUD cross during two different conditions, and you focus on how spreads typically respond.
- Lower liquidity window (example: fewer active participants)
- Assumption: Fewer orders are waiting at the best bid and ask.
- Mechanism: With thinner depth, a single trade can move the best prices more. To protect against adverse selection and maintain risk limits, liquidity providers may widen the bid–ask spread.
- Observable implication: If you compare snapshots close in time, you should often see a wider spread when liquidity is lower.
- Higher volatility window (example: faster price changes)
- Assumption: Price changes are larger over short intervals.
- Mechanism: Market makers may widen spreads so that their expected profit over the holding period compensates for faster uncertainty.
- Observable implication: Even if liquidity is similar, higher volatility can still increase the spread.
- Execution and fee structure (example: quoted spread vs all-in cost)
- Assumption: Two providers offer different fee models.
- Mechanism: Provider A might quote a smaller bid–ask difference but charge a commission; Provider B might quote a larger difference but lower or no commission. The “spread” number alone cannot tell you the full cost.
- Observable implication: You verify by measuring your all-in cost from execution reports rather than relying on the spread quote alone.
Limitations and failure modes
Several limitations can make spread explanations look inconsistent:
- Timing mismatch: Spread is time-sensitive. A quote you saw earlier may differ from what you get at execution.
- Hidden costs: Even with the same quoted spread, commissions, financing-related charges (where applicable), and slippage can change total cost.
- Order size effects: Large orders can move prices through the book, effectively widening the cost beyond the displayed best spread.
- Venue differences: Different routing paths can yield different realized spreads, so two users can observe different outcomes at the same moment.
- Correlation traps: Historical relationships between volatility and spreads do not guarantee future behavior; regimes change.
Verification and next question
To independently verify what affects spreads for AUD crosses, use a self-check that avoids assumptions:
- Record time-stamped bid and ask quotes (or a consistent spread proxy) and compare them across market states (calm vs fast price movement).
- Compare quoted spread with real execution outcomes (fill price vs expected) to measure slippage.
- Note order size and execution type you used, since these can change the realized cost.