What rollover means in major pair trading
Rollover is the overnight adjustment applied to a forex position because the position is effectively “carried” to the next settlement date. In simplified terms, the amount you see is tied to the interest-rate difference between the two currencies in the pair, plus any provider-specific adjustments (such as spreads or commissions built into the swap quote).
A major currency pair typically involves currencies that have well-known reference rates. Still, the exact rollover charged or credited is not just the interest differential; it also depends on how a provider converts those rates into a daily number, how it handles weekends and holidays, and how it applies its pricing model.
The core mechanics: inputs and calculation structure
A common way to explain rollover calculation uses three ideas:
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Interest-rate differential as the driver. If one currency’s reference rate is higher than the other’s, then in many convention frameworks the long position on the higher-yield currency may receive a positive swap and the opposite side may pay a negative swap. The reverse can also occur depending on which currency you are long.
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Conversion into an overnight amount. Providers usually turn the reference interest-rate difference into a daily figure (for example, by using a day-count convention that maps annual rates to a daily rate). They then apply that daily figure to your position size, scaled by a contract convention that links lots to notional exposure.
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A provider adjustment and display convention. Even when the interest-rate inputs are similar, the displayed rollover can differ because providers may apply their own adjustment factors, rounding rules, swap formulas, and any internal markup included in the swap quote.
Triple-swap convention (extra days)
Many markets follow settlement rules that create more than one day of “carry” when holding through a non-settling period. This is why rollover is often described as “triple-swap” on certain days: the overnight charge or credit may be calculated for an additional number of days (commonly three instead of one) to reflect the longer holding period.
A simple example model (assumptions stated)
To make the mechanics concrete without relying on live rates, assume:
- You hold one position overnight on a day with normal rollover.
- A provider converts an annual interest-rate differential into a daily rate using a day-count convention.
- Rollover is then proportional to the notional exposure and the daily differential.
Under those assumptions, the rollover you receive or pay would be proportional to: (daily rate derived from annual differential) × (position notional) × (provider sign convention).
If you hold through a day with “triple-swap,” the provider effectively multiplies the overnight component by the extra-day factor (for example, using three days instead of one).
Limitations, failure modes, and what can change
Several limitations commonly cause rollover calculations to differ from what a trader expects:
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Rollover is provider-specific. Even with the same underlying interest-rate differential, providers may apply different conversion methods, rounding, or adjustments to the quoted swap.
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Day-count and scheduling conventions matter. The daily-rate conversion and the exact days that trigger extra-day rollover depend on settlement and provider scheduling. If the “triple-swap” day differs across providers or jurisdictions, the observed rollover can differ.
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Displayed rollover may include more than interest. Some providers incorporate fees, commission-like components, or internal pricing adjustments into the swap quote. That means the “interest-rate differential only” model can be incomplete.
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The sign can flip with position direction and rules. Whether you are charged or credited depends on whether you are effectively long the higher-yield currency (under the provider’s convention) and on how the provider maps your direction to swap sign.
How to verify rollover claims independently
Because rollover depends on provider-specific pricing, independent verification usually works best by comparing documentation and observed swap lines:
- **Use the provider’s own swap/rollover schedule. ** Look for a table that lists swap amounts by currency pair and direction, including the special-day (often triple) rule. - **Check the recorded rollover date and time basis. ** The swap may post at a specific time; if your platform captures the position across day boundaries differently than you assume, the applied rollover can differ. - **Reconcile with a “difference in rates” back-of-the-envelope model.