Direct answer: what determines rollover for quote currency?
Rollover (often called swap) for a forex position is the interest-related carry cost or credit that gets charged (or paid) when a trade is held overnight. For the specific case of “quote currency,” the key idea is that the interest differential between the two currencies is translated into an amount using the pair’s quote currency, then applied according to the broker/platform’s rollover timing and conventions.
In practice, rollover is not a single universal formula visible to every user. The stable mechanism is: (1) determine the interest-rate inputs implied by the pair, (2) compute the carry over the holding period (typically one day, with special handling on rollover days), and (3) convert that carry into the cash amount in the quote currency (or account currency, via conversion).
Mechanism: interest-rate inputs and “quote currency” conversion
1) Start with the two currencies’ interest rates
A forex pair has a base currency and a quote currency. When you hold the position, you are economically long one currency and short the other. The carry you receive or pay is driven by the interest-rate difference between those two currencies.
A common simplification used for understanding is:
- Carry per day ≈ (Interest rate of long currency − Interest rate of short currency) ÷ 360 (or another day-count convention) × Notional
The exact day-count basis (for example, 360 vs 365) and the interest-rate sources (for example, money-market proxies) depend on how the provider defines rollover.
2) Apply the rates to the side you effectively hold
Whether rollover is charged or credited depends on whether you are effectively long or short the currency with the higher interest rate (again, according to the provider’s interest interpretation).
3) Translate the carry into quote currency terms
Even if the interest differential is conceptually about the two currencies, the operational output is a monetary amount. Because the pair is quoted with a specific quote currency, the provider typically expresses the cash impact using that quote currency convention, then may convert it into your account currency.
That translation usually involves:
- Using the trade size (notional)
- Using the pair price (or an internal reference rate) for conversion
- Applying provider-specific rounding and any additional adjustments
So when people say “rollover for quote currency,” they are usually referring to how the interest differential is ultimately mapped into an amount governed by the quote currency side of the pair.
Evidence or example: a self-checkable, assumption-based calculation
Because different providers implement rollover differently, the best way to verify the concept is to compute a simplified estimate using explicit assumptions.
Example assumptions (for learning only):
- You hold one position overnight
- The provider uses a daily accrual convention and a fixed day-count denominator
- The interest differential is treated as known from the provider inputs
- The provider converts the result into the quote currency using the pair’s reference price
A learning-style workflow:
- Identify base and quote currencies for the pair.
- Decide which currency is effectively “long” and which is “short” for your position direction.
- Compute an interest differential (rate_long − rate_short).
- Convert that differential into a daily carry amount using the provider’s day-count denominator.
- Apply conversion to reach the quote-currency cash impact (or your account currency, if needed).
If your computed estimate is close but not exact, the remaining gap typically comes from provider conventions: different day-count bases, the exact interest-rate proxy, operational timing, price references, and provider adjustments.
Triple-swap convention (material limitation)
A common rollover limitation is the “special rollover day” convention. Many platforms apply a triple-swap approach around days when markets are closed, meaning the overnight carry charge/credit can be multiplied (often by 3) for certain holding transitions. This is not a universal rule, but it is a frequent convention.
Failure mode to watch: if you estimate rollover as “one day only,” you may be off materially around those transitions because the platform may accrue more than a single daily period.
Limitations and risks: why rollover may not match expectations
Provider-specific inputs and adjustments
Rollover depends on provider-defined interest-rate inputs and any operational adjustments. Two providers can use different proxies or conversion approaches, so identical-looking positions may produce different rollover outcomes.