Rollover: the basic idea
Rollover (also called a swap or overnight interest adjustment) is the mechanism used to carry a currency position from one trading day to the next. In foreign exchange, a position is typically booked as a spot trade with an implicit financing component. When you hold it, the financing cost or benefit is approximated by the interest-rate difference between the two currencies in the pair.
For AUD crosses (a trade where AUD is paired with another non-USD currency, such as AUD/JPY, AUD/EUR, or AUD/GBP), the same principle applies: the rollover you receive or pay is linked to:
- the interest rate inputs for AUD,
- the interest rate inputs for the other currency,
- and the provider’s conversion and quoting conventions for cross rates.
Because rollover is derived from inputs and conventions, it is not a single universal number. Two providers can show different rollover amounts for the same AUD cross, even if they use similar underlying rate concepts.
The standard mechanics: interest-rate inputs and the cross-rate step
A useful way to understand AUD-cross rollover is as a two-part process.
1) Compute the interest differential
Conceptually, rollover compares expected financing for the two currencies. If the currency you are long has a higher relevant interest rate than the currency you are short, the rollover is more likely to be a credit; if it is lower, it is more likely to be a debit. The sign (pay vs receive) depends on which side of the pair you hold.
2) Apply the cross conversion convention
For AUD crosses, the “other currency” is not paired with AUD via USD in the contract itself, but many data providers and internal pricing systems still rely on cross-rate consistency. This means the rollover for an AUD cross is often produced by combining rate conventions for both legs (AUD and the other currency) using the provider’s internal method for cross-rate pricing.
So, while the interest differential is the key driver, the final rollover amount you see is affected by how a provider:
- maps its interest-rate inputs into its swap/rollover model,
- determines which day-count and compounding conventions to use,
- converts the result into the account currency and quoted units.
“Triple swap” conventions and day-count effects
Rollover is typically calculated per holding period. That matters because not all calendar days behave the same.
A common convention in FX markets is that positions held over non-trading days are charged for a longer effective period. For example, when markets close over a weekend, the rollover that accrues for that extended gap can be applied as a larger multiple (often referred to as “triple swap,” though the exact multiple depends on the platform and convention). The important point is that the rollover shown on your platform may reflect an adjusted number of days, not simply a one-day interest figure.
Additionally, day-count conventions (how many days are assumed in the interest calculation) and the exact timing of when rollover is applied (server time) can shift the effective accrual period. That can change the amount you pay or receive on the days before/after market closures.
Broker/provider adjustments: why the same concept can show different numbers
Even if you agree on the interest-rate logic, providers may still adjust the final rollover they display. Common sources of variation include:
- swap tables derived from their internal pricing,
- a markup or fee embedded in rollover rather than shown separately,
- differences in how they convert between currencies and lot sizes,
- how they handle holidays and non-standard settlement periods.
Because these elements are provider-specific, the only fully reliable way to verify the calculation for a specific AUD cross is to compare the platform’s displayed rollover amounts with its own stated conventions (often found in trading conditions, FAQs, or contract specifications).
Material limitations and failure modes
Limitation 1: rollover is not a performance forecast
Rollover calculations are mechanical under the provider’s current pricing conventions. They do not guarantee future results, because future interest inputs and pricing conditions can change.
Limitation 2: displayed rollover depends on execution and timing
If you enter or exit around rollover application times, the effective holding period can differ.