Direct answer
Rollover for Sterling crosses is typically calculated from the interest-rate difference between the two currencies in the pair, expressed as a daily swap. Providers then convert that theoretical value into the platform’s quoted swap amount (credit or debit) using their own conventions, including how the “swap day” is handled (often a triple-swap on a particular rollover day).
Mechanism: what “rollover” means for Sterling crosses
A Sterling cross is a currency pair where one side is a Sterling-related currency (GBP) and the other is a different currency (for example, EUR/GBP or USD/GBP). In many retail FX setups, trades do not settle like physical spot transactions; instead, a position held past a provider-defined cutoff date earns or pays a financing adjustment called rollover (also referred to as a swap).
A practical way to model rollover is to treat it as the net effect of “carrying” each currency against the other:
- Currency A (GBP or the other currency) has an associated short-term interest rate expectation.
- Currency B has its own associated short-term interest rate expectation.
- The difference between these rates drives whether holding the position is generally credited or debited.
For a cross, the interest-rate inputs are typically derived from standard money-market rates (or equivalent interbank benchmarks) for each currency, then mapped into a daily rate using an agreed day-count convention. The exact benchmark choice is provider-specific, but the structure is usually: daily carry ≈ (rate of one currency − rate of the other currency) × the position notional, with sign depending on the long/short direction.
Mechanics: how providers turn the interest gap into a quoted “triple-swap” rollover
1) Interest-rate difference becomes a daily carry
Assume a hypothetical daily carry rate for the pair that results from the interest-rate gap, after day-count conversion. If you hold a position for one provider day (the period between rollover cutoffs), the theoretical rollover is proportional to:
- the trade’s notional size (how much of the base currency conceptually is involved)
- the daily carry rate
- the direction of the trade (long vs short), which determines whether you receive or pay the net carry
2) Swap sign and “credit vs debit”
Even if the interest-rate difference is favorable to one currency, the rollover outcome depends on whether you are effectively long or short the higher-yielding side. Providers apply the sign so that, for example, holding a position that is economically equivalent to borrowing the lower-rate currency and lending the higher-rate currency tends to produce a credit, while the opposite tends to produce a debit.
3) Bid/ask and provider adjustments
Providers often quote different swap amounts for buying vs selling (because the provider may apply bid/ask spreads to the swap legs). They may also apply an adjustment or markup so that the swap you see on the platform matches the provider’s internal pricing for financing.
So, two traders with the same notional and direction but using different providers can see different rollover amounts.
4) Triple-swap convention
Many platforms apply a special convention on a particular rollover day (often associated with the weekend break in settlement cycles). Conceptually, instead of paying/earning for one day, the platform charges or credits an additional two days’ worth of carry on that rollover event.
Material assumption for examples: “triple-swap” means the daily swap is multiplied by three for that rollover date. The actual multiplier and which day triggers it can vary by provider and instrument.
Evidence or example (with explicit assumptions)
Because the exact swap formula depends on provider documentation and the specific rates used, the safest way to verify the calculation is to work from the provider’s displayed swap rates.
Example model (illustrative, not using live provider numbers):
- Assume the platform lists a daily swap for a Sterling cross of +0.01% of notional when holding the position in one direction, and −0.01% in the opposite direction.
- You hold the position through one normal rollover day: theoretical rollover = notional × 0.01%.
- You hold it through the special rollover day: triple-swap applies, so theoretical rollover = notional × 0.01% × 3.