What “rollover” means in this context
Rollover (often called swap) is the cost or credit you experience when you keep a position open beyond the platform’s daily rollover time. In simple terms, it represents an interest-rate adjustment for holding a leveraged currency exposure overnight.
When people connect rollover with “pair volatility,” they are usually describing a relationship in outcomes: on more volatile days, the size or direction of price moves may change how noticeable the rollover becomes relative to other P&L sources. But the mechanics of rollover are not derived from volatility in the statistical sense; they are derived from interest-rate conventions, provider adjustments, and timing.
Basic rollover mechanics (interest inputs)
A currency pair can be treated as holding one currency and financing the other. The rollover value is therefore tied to the interest-rate differential between the two currencies involved.
A common way to think about the inputs is:
- Choose the interest rate associated with each currency (often represented as an annualized rate).
- Convert the differential into a daily amount using the pair’s day-count convention (for example, “annual rate divided by 360 or 365,” depending on convention).
- Apply the direction: being “long” one currency vs “short” the other flips whether you typically receive or pay the net interest.
- Scale by position size and contract specifications (how much base/quote currency exposure each lot represents).
Assumptions matter. For any numeric example you do, state:
- The annualized rates used by the provider (or the benchmark rates their published swap formula references).
- The provider’s day-count and compounding assumption (if any).
- The contract size used to translate “per unit” into your position notional.
Broker/provider adjustments and triple-swap conventions
Even with the same underlying interest-rate differential, the credited/debited rollover can differ because providers apply their own operational conventions.
Typical adjustment areas include:
- Markups or internal pricing: the provider may add a spread to the theoretical interest differential to reflect execution, risk, or internal valuation.
- Rounding rules: the platform may round to the account currency or to a fixed decimal precision.
- Cut-off timing: whether the rollover applies depends on whether your position is open at the cut-off time, not when you entered intraday.
A triple-swap convention is a special case where the swap charged or credited over a longer gap (often covering non-business days) is applied as an effective multiple. Many platforms implement this on specific calendar days so that the cost/credit accounts for a longer period in one posting. The key verification step is not to assume the multiplier is always three; instead, use the provider’s published rollover schedule for the instrument and the relevant day.
Simple check model (non-numeric)
To independently verify a rollover calculation for a given instrument and account:
- Identify the published swap rate format (e.g., per lot, per unit, or per notional; and whether it is shown as a credit/debit depending on direction).
- Confirm the position direction (long/short) and whether the shown swap rate already accounts for that.
- Apply the contract size conversion to get the expected swap in account currency.
- Apply the calendar rule (normal vs triple-swap day) based on the platform’s rollover schedule.
Limitations and failure modes
At least four material limitations often cause “rollover surprises”:
- Volatility can dominate relative impact: even if the rollover math is correct, sudden price moves can swamp rollover effects, making it appear inconsistent with expectations.
- Calendar exceptions: weekend/holiday conventions (including triple-swap) can change the multiplier, so copying a “typical day” calculation to a special day is wrong.
- Timing/cut-off dependence: if you open or close near rollover time, the platform may apply the swap based on the cut-off rule, not your intention.
- Hidden provider conventions: the provider may use specific benchmark definitions, markups, rounding, and account-currency conversion steps. If you do not match those conventions, your independent calculation will not align.
How to verify without relying on predictions
Because rollover involves provider-specific schedules and conventions, the most reliable verification method is procedural:
- Use the provider’s published rollover (swap) rates and schedule for the exact instrument.
- Compute expected swap for your actual position size and direction using the instrument’s contract specification.
- Check what happens on normal days vs special multiplier days.