Direct answer
Rollover for NZD/USD is the interest-like charge or credit applied when you hold a currency position overnight instead of closing it at the same business day. In concept, it is driven by the interest-rate differential between New Zealand dollars (NZD) and US dollars (USD), then adjusted by the provider’s pricing conventions (including markups and swap timing rules).
Because rollover is provider-specific in practice, the only way to “calculate it” for a real account is to map the provider’s stated rollover components to the general formula structure used by FX swap conventions. This article explains that structure so you can independently check the inputs you’re given.
Mechanism or definition: what “rollover” means
An FX spot trade can be viewed as two parts: exchanging currencies today, and implicitly agreeing to reverse that exchange later. When the position is carried into the next value date, the agreement is effectively replaced by an FX forward price (or, equivalently, by a swap). The cash impact you see as “rollover” is the monetary result of that swap versus holding cash without the trade.
For NZD/USD, the key conceptual driver is the relative “cost of carry”:
- If NZD interest rates are higher than USD rates, the position that is long NZD versus USD tends to earn rollover (credit), all else equal.
- If NZD interest rates are lower, the same long-NZD position tends to pay rollover (debit).
However, “all else equal” rarely holds, because providers layer on the pricing and settlement conventions they use.
Simple model: inputs and how a provider-adjusted calculation typically looks
A practical way to reason about rollover is to break it into inputs and conventions.
1) Two interest legs (the differential)
Many rollover explanations boil down to an interest-rate differential between the two currencies, applied over the overnight period. In a simplified educational model, you can think of it as:
- An “NZD leg” based on NZD short-term funding assumptions.
- A “USD leg” based on USD short-term funding assumptions.
- The net is based on the difference.
This is often operationalized via the spot-forward relationship for FX swaps, or via an equivalent swap-rate approach. The important point is: you need both currencies’ rate assumptions to get the net carry.
2) Contract timing convention (day count and when the swap is applied)
Overnight carry is not a single universal number. It depends on when the value date rolls and how the provider counts days (day-count conventions). This matters because interest over “one day” is not always treated as exactly 1/365 in every internal model.
3) Provider adjustments (markup and pricing methodology)
Providers may adjust the theoretical differential using their internal pricing, liquidity sourcing, and fee or markup components. So the rollover you see is not just “market differential” but “differential plus provider-specific adjustment.”
A general structure that matches many educational explanations is:
- Rollover cash = (swap points / FX rate reference) × position notional
- where “swap points” come from an interest-rate differential model and then are adjusted by the provider’s conventions.
Because the exact parameters are account-dependent, you typically verify by checking the provider’s displayed rollover rates or swap charges/credits for NZD/USD and matching them to the notional size and timing shown in your platform.
4) Triple-swap (timing exceptions)
Many FX rollover systems apply special handling on certain days (often when there is a weekend or longer-than-usual break between value dates). In those cases, the system charges or credits an amount equivalent to multiple standard overnights. If you hold NZD/USD through such a rollover window, you may see roughly larger rollover than a normal day.
This is a major limitation of any “single overnight” calculation: the number you observe may be the product of multiple daily equivalents due to swap-timing rules.
Evidence or example: a checkable calculation setup (assumptions first)
Because there are no live rates here, the most useful example is a verification template.
Assume:
- You have an NZD/USD position with a known notional size (the platform shows this).
- Your provider states a rollover rate expressed in swap points (or directly as a rollover amount per day).
- The rollover is applied once per day in the platform’s settlement convention.