How Rollover Is Calculated for Commodity Currencies

Define rollover (swap) before the calculation

Rollover (often called “swap”) is the carry cost or carry credit that can be applied to a forex position when it is held past a daily cutoff. In many retail trading setups, the amount is conceptually tied to the interest-rate differential between the two currencies in the pair.

A key point is that “calculated from interest rates” does not mean there is one universal formula visible to all users. The core idea is stable, but the exact number depends on implementation details such as the provider’s swap table, timing, and rounding.

The core mechanics: interest-rate differential and day-by-day application

At a high level, rollover comes from comparing the implied short-term funding costs of the two currencies. If the base currency’s interest factor is higher than the quote currency’s, the direction may produce a carry credit for one side and a carry cost for the other. The sign and size depend on which currency is “long” in the position.

When you hold a position overnight, the provider applies a value for that day, typically expressed per lot or per unit of notional. The daily application means the rollover you receive (or pay) is not just one-time; it can accumulate, with each day potentially changing the amount.

Assumptions for a generic example (for explanation only):

You hold a position across a single rollover cutoff.
Rates and the provider’s swap parameters remain constant for that day.
The pair uses a provider convention that applies one “daily swap” amount for that specific rollover event.

Under these assumptions, the calculation is:

Determine the interest differential inputs used by the provider.
Convert that differential into a monetary value using the provider’s contract specification (how lot size maps to notional exposure).
Apply the correct sign based on whether your position is effectively long or short the relevant currencies.

Provider adjustments and the “triple-swap” convention

Two implementation features commonly change the realized rollover.

1) Broker or platform adjustments

Many platforms do not simply compute a theoretical interest differential and then charge exactly that. Instead, they use their own published swap/financing parameters that incorporate costs and internal pricing assumptions. Even when the underlying driver is still the interest-rate differential, the provider-adjusted value can differ from a purely theoretical computation.

2) Triple-swap on specific rollover days

Some setups apply a larger rollover amount on certain days (commonly framed as “triple swap”). The purpose is to account for the longer gap in market settlement behavior over a weekend or non-working days.

For an explanatory triple-swap example (assumptions only):

Suppose a “normal” daily rollover amount for a pair is R.
On the triple-swap rollover event, the platform may apply approximately 3×R (or an equivalent convention) instead of 1×R.
If R is a debit for your direction, triple-swap typically makes that debit larger for that event; if R is a credit, it makes the credit larger.

Evidence through verification: what to check independently

Because exact formulas and parameters are provider-specific, the most reliable way to verify “how rollover is calculated” for commodity currency pairs is to check the platform’s own swap documentation and current swap table entries.

You can independently verify the mechanics by:

Identifying the pair and your position direction (which currency is effectively long/short).
Locating the provider’s swap values for that instrument and direction.
Confirming the rollover timing used by the platform (daily cutoff).
Checking whether the instrument follows a triple-swap convention on specified rollover days.
Comparing the applied rollover charges/credits in the account history for multiple days under similar conditions.

If the amounts change between days, that indicates either rate-related input changes or that the provider updates its swap parameters.

Material limitations and failure modes

Provider-specific parameters: Two providers can produce different rollover amounts for the same pair because they may publish different swap/financing parameters.
Timing risk: If a position is opened or closed near the cutoff time, the rollover event may differ from your expectation.
Rate changes: Even without changing your position direction, the interest differential inputs can change over time, causing rollover to vary.