Direct answer
Rollover in EUR/USD versus GBP/USD is calculated from the interest-rate difference between the two currencies in each pair, adjusted for the account/provider’s pricing conventions (including how they convert rates into a per-day swap) and any special timing rules (such as larger swap on certain days). The “direction” also matters: being long one currency earns a different amount than being short it.
Mechanism and definition
Rollover (swap) is an overnight adjustment applied to a forex position held beyond the broker’s cutoff time. It is meant to reflect the economics of holding one currency against another: you effectively earn the interest associated with the currency you are long and pay the interest associated with the currency you are short, net of how the provider translates rates into tradable contract terms.
For a currency pair, the calculation is commonly described in three layers:
- Interest-rate inputs: For each currency, there is a reference interest rate (or a proxy) used to estimate overnight carry.
- Pair-direction netting: A long position in a pair implies you are long the base currency and short the quote currency; a short position flips the sign.
- Provider conventions and conversion: Brokers may convert reference rates into a swap amount using the instrument’s contract size, quote conventions, day count, and sometimes an additional adjustment or markup.
With EUR/USD and GBP/USD, the core difference is the interest-rate difference between EUR and USD versus GBP and USD. Even if the USD side is the same reference, EUR’s and GBP’s reference rates are not generally equal, so the carry—and therefore rollover—will differ.
Triple-swap conventions
Some market conventions apply an extra rollover amount on certain weekdays (often discussed as a “triple swap”), because the position spans more calendar days when markets are closed. Whether and how this appears depends on the provider’s rollover schedule and the instrument’s contract rules.
Evidence or example (with explicit assumptions)
Because providers differ, you should verify the exact formula in the provider’s instrument specification, but a generic comparison looks like this:
Assumptions for this example (purely illustrative):
- The provider uses a daily carry rate derived from reference interest rates.
- “Daily” means a per-day fraction, not a full calendar-day rate.
- The base/quote interest-rate difference determines the sign and magnitude.
- Triple-swap occurs on one specific day in the provider’s schedule.
Step 1: Compute the interest difference per pair (conceptually)
- For EUR/USD: use (EUR reference rate − USD reference rate) as the carry driver.
- For GBP/USD: use (GBP reference rate − USD reference rate) as the carry driver.
If (EUR − USD) is larger than (GBP − USD), then all else equal, the EUR/USD rollover will tend to be larger for the same trade direction.
Step 2: Convert the carry into a swap-per-night amount (conceptually) Providers translate the interest differential into a money amount using contract size and a day-count convention (and sometimes an adjustment for their pricing).
Step 3: Apply timing rules If the position is held over the provider’s “extra day,” the overnight rollover can be multiplied (e.g., effectively applying the normal daily rollover three times for that posting), creating a larger debit or credit than a typical day.
Material limitations and failure modes
Rollover amounts you see are not guaranteed to be a direct, transparent “interest difference times size” outcome. Common failure modes include:
- Provider pricing adjustments: Some providers apply a markup/markdown or use different mid-to-execution rate handling than the reference-rate intuition suggests.
- Cutoff time and calendar effects: If the position is opened/closed near the rollover cutoff, the number of affected days may differ from what you expect.
- Contract specifications: Contract size, whether the account shows swap as a per-lot figure, and how conversion into the account currency is done can change the displayed amount.
- Triple-swap schedule differences: The “extra” rollover day may vary by provider, and the factor may not look identical across platforms.
Because of these, two providers can show different rollover outcomes for the same EUR/USD and GBP/USD direction.