Direct answer
AUD crosses (currency pairs where the Australian dollar is one side and the other currency is not USD) have limitations mainly because the pair’s behavior is not governed by a single stable relationship. Their movement depends on how two underlying exchange-rate relationships interact, and those relationships can shift across regimes. Any expectation built from past behavior can fail because markets, liquidity, and trading frictions change over time.
Mechanism and definition
An AUD cross expresses the value of AUD against a second currency using exchange rates for the two currencies involved. In practice, you can think of it as combining two “legs”: AUD’s relative value versus the other currency, which is influenced by multiple drivers (for both economies) rather than a single factor.
A key implication follows from this definition: the same AUD crosses can behave differently at different times because the relative strength of AUD versus the other currency can change due to shifting macro expectations (such as interest-rate outlooks or risk sentiment) and due to microstructure differences (such as liquidity and trading costs). Even if the concept is mechanically consistent, the inputs that determine outcomes are variable.
Evidence or example (with explicit assumptions)
Assume you observe that, over a period, AUD tends to move in a certain direction relative to a target currency. That does not guarantee future alignment because at least three things can change:
- The relationship can weaken or reverse when expectations for AUD and the other currency diverge.
- Costs and execution quality can change (for example, wider spreads or different fill quality during volatile periods).
- Market participants may reprice risk faster or slower across instruments.
For an example of “relationship breakdown,” consider a simple scenario: AUD strength previously coincided with strength in the other economy, but later the other economy’s outlook shifts (for instance, expectations for its policy path move differently). The AUD cross can then move opposite to what the earlier pattern would suggest, even though nothing about the pair’s definition has changed.
Limitations and risks
1) Uncertainty from changing relationships
AUD crosses are exposed to correlation or dependence changes between the two legs that form the pair. Relationships that appear stable in historical data can break when market conditions shift.
2) Costs and execution can dominate small effects
Even without assuming any particular broker or platform, trading frictions matter. Spreads, commissions (if any), order routing, and slippage can alter realized outcomes versus what you might infer from mid-market intuition. In volatile or low-liquidity conditions, this gap can widen.
3) Historical performance does not establish future results
Historical relationships are descriptive, not predictive. A pattern observed in one sample window may not apply after regime changes, structural shifts, or changes in how traders hedge and price risk.
4) Jurisdiction and market rules can affect implementation
Actual results can differ across venues and jurisdictions because rules for trading, leverage, margining, and product availability can vary. This means verification must be based on the specific legal and operational context, not a general concept.
Verification and next question
To independently verify how AUD crosses “work” in your context, focus on what is measurable and variable: compare behavior across multiple time windows, account for trading costs and execution conditions, and avoid treating any past relationship as durable. A useful next question is: under what market conditions do AUD crosses deviate most from the behavior implied by prior observations?