Direct answer
Rollover (often called the “swap” or “swap rate”) for an EUR/PLN position is a net overnight interest amount. In general terms, it is calculated from the interest-rate expectations for EUR and PLN, converted into a per-day value, then adjusted by the market or provider’s swap formula. On certain days—commonly linked to the weekend—some platforms apply a “triple-swap” convention, multiplying the normal overnight amount.
The mechanism: what rollover means
A forex position is effectively a short exposure in one currency and a long exposure in the other. If you keep that position past an overnight cut-off, the provider records the cost or benefit of carrying those currency legs. Conceptually, rollover is based on:
- Interest-rate difference between the two currencies (EUR vs PLN).
- Day count and timing (how the overnight amount is prorated).
- Swap conventions used by the provider or platform.
- Provider adjustments (their pricing of execution spread, funding, or internal markup/markdown).
Because providers publish rollover in different formats, you will usually see it as either:
- a listed swap rate per unit/position size, or
- a net swap amount in the account currency for holding overnight.
Either way, the underlying idea is the same: it reflects the net cost/benefit of holding the position one day.
Interest-rate inputs and how they become an overnight number
1) Start with a benchmark-based interest view
For many rollover calculations, the starting point is a benchmark representing “market funding” for each currency. The provider uses a EUR benchmark (for the EUR leg) and a PLN benchmark (for the PLN leg), then computes a difference. A simplified educational model looks like:
- Net interest ≈ (EUR interest leg) − (PLN interest leg) (or the reverse, depending on long/short orientation)
2) Convert to the position’s overnight amount
Even with the same interest difference, two additional factors determine the actual overnight rollover charged/credited:
- Direction (long vs short): If you are long EUR/PLN, you are typically long EUR and short PLN; reversing the position reverses the sign of the net interest.
- Position size and unit conversion: Providers convert the interest difference into a monetary value using their contract specifications (for example, how many currency units correspond to one “lot”).
3) Apply provider-specific adjustments
Two providers can show different rollover values even when using the same general benchmark idea. This happens because of provider-specific components such as:
- how they translate the benchmark into their internal pricing,
- any markup/adjustment in their swap formula,
- the way they incorporate execution and liquidity costs.
Therefore, the only fully correct “calculation” for a given EUR/PLN rollover figure is the one consistent with the provider’s published swap formula and contract specification.
Triple-swap convention: why some days differ
Many platforms apply an exception on days just before periods when the market carry is effectively extended (most commonly, the weekend). In practice, this can mean:
- the normal daily rollover is multiplied (often described as “triple”) for a specific weekday,
- or the rollover is computed using an extended carry horizon.
Even if you understand the base overnight model, the triple-swap rule changes the amount for those specific days. This is a major limitation of any attempt to project rollover from a single day’s rate.
Evidence or example (with explicit assumptions)
Below is a checkable example using a simplified model. It is not a guaranteed formula for any specific provider.
Assumptions (for illustration only):
- You have a long EUR/PLN position.
- The provider’s swap calculation is based on a daily net interest difference.
- The listed swap amount for a normal day equals some base daily value.
Normal day (no triple)
- Start from the provider’s base daily swap for EUR/PLN.
- Apply direction (long vs short) as defined by the provider.
- Multiply by the position size per the contract.
Triple-swap day
- Take the same base daily swap.
- Multiply by 3 (or use the provider’s stated multiplier/extended-day logic).
- Apply the same direction and position size rules.
What to verify independently: whether the provider uses a literal “triple = 3× normal day” multiplier, or whether it computes using an extended carry period that might not match 3× exactly in all cases.