Direct answer
Rollover (also called swap) for USD/MXN is the net interest effect of holding a position overnight, calculated from the interest-rate difference between USD and MXN and then adjusted by how a specific provider applies swap pricing. The exact numbers shown to you depend on provider-specific conventions such as contract size, pricing sources, and when triple swaps are applied.
How rollover works for a currency pair
Definition. In forex, a spot transaction is typically settled as if currencies are exchanged “now,” while the position is effectively carried forward to future value dates. The overnight carry cost or benefit is reflected as rollover, expressed in account currency and typically applied per position side (long/short).
Core mechanic (interest differential). For USD/MXN, the provider estimates the relative funding cost of holding USD versus holding MXN. If the reference USD funding rate is higher than MXN’s, the carry direction often changes depending on whether you are effectively long or short the USD component in the pair. In general terms, the rollover amount comes from:
- an interest-rate input for USD,
- an interest-rate input for MXN,
- a conversion into a per-day carry using the pair’s pricing conventions,
- a sign change depending on whether your position benefits from or pays the interest differential.
Daily application and compounding assumption. Many systems apply rollover on a daily basis using an annualized rate converted to a daily amount (for example, by dividing by a day-count convention). The result is then scaled to the position notional and contract specification.
Evidence-style example (with explicit assumptions)
Because different providers can use different inputs and conventions, it’s best to understand the calculation as a model you can verify against your platform’s displayed swap formula.
Assumptions for the example (not live data):
- You hold one USD/MXN position overnight.
- The provider converts annualized interest rates into a daily carry.
- The daily carry is proportional to the interest-rate difference: (USD rate − MXN rate).
- A positive carry means you receive rollover; a negative carry means you pay.
Model calculation steps:
- Pick the provider’s reference USD rate and MXN rate as used for swap pricing.
- Compute the interest differential: USD_rate − MXN_rate.
- Convert that differential into a daily factor using the provider’s day-count convention.
- Apply it to your position notional (contract sizing determines the scaling).
- Apply the direction: if your position corresponds to effectively funding USD, the sign may differ from if it corresponds to effectively funding MXN.
Triple-swap convention (material variation). Many platforms apply an additional rollover on certain rollover days (often described as “triple swap”). In the simplified view, a triple-swap day multiplies the usual daily rollover by roughly three, reflecting extended holding over a weekend or other non-standard value-date gap. This means two days of similar market conditions can produce very different rollover amounts across days.
Provider adjustments and typical failure modes
Provider adjustments. Even with the same pair and direction, the amount you see can differ because providers may:
- use specific reference rates (and may refresh them at set times),
- adjust for pricing add-ons (such as operational or liquidity components) included in their swap pricing,
- round results to the account’s tick/precision rules,
- compute rollover using the platform’s contract definition and notional methodology.
Limitation: the shown number is not a universal formula. A platform’s displayed rollover rate can embed assumptions that are not visible unless you consult the provider’s swap specification. Therefore, you should treat the rollover as a provider-specific implementation of the interest-differential concept.
Limitation: day-count and triple-swap rules can dominate. For many accounts, whether rollover is applied as usual or as a triple swap can create large apparent differences. Even if the interest differential is stable, the calendar-based rule can change the final amount.
Limitation: execution and costs affect net outcomes. Rollover is only one component of total position cost or benefit. Execution-related factors (for example, how spreads are handled when you enter and exit) can influence the net result even if rollover itself is computed correctly.
Verification and next question
To verify rollover for USD/MXN independently:
- Check the provider’s swap/rollover documentation for your account (definitions, rate sources, and day-count conventions).