What is a worked example of Forex Swap?

Definition and scope

A Forex swap (often called an “overnight” or “rollover” adjustment) is the amount added to, or deducted from, a trader’s account when they keep a leveraged currency position open beyond one trading day.

Important: in real accounts, the exact swap charge depends on provider-specific contract terms and on changing market rates. So a “worked example” is not a live quote; it is a numerical demonstration using explicit assumptions that you can replace with your own rates and terms.

Mechanism: what the calculation is trying to capture

At a high level, a currency position can be viewed as holding one currency and effectively borrowing the other. The swap adjustment approximates the relative interest costs and benefits between the two currencies over the holding period.

To keep the example verifiable, separate the mechanics from variables:

• Stable mechanics (model): swap relates to interest-rate differentials and depends on whether you hold the “base” currency long or short.
• Variable conditions (inputs): interest rates (or the provider’s derived values), contract specifications (lot size, quote conventions), and the timing/number of rollover days.

Assumptions for a worked example

Because no real-time data is provided here, the example uses hypothetical inputs and clearly labeled assumptions:

1. You hold a one-lot position in EUR/USD.
2. Lot size is 100,000 units of the base currency (EUR), a common market convention.
3. The position is kept for one overnight period.
4. The swap is computed using an interest differential approximation.
5. We assume an annualized differential that we will translate into an overnight amount.

Worked numerical example (hypothetical)

Given (assumptions)

• Position: Long EUR/USD (buy EUR, sell USD).
• Time held: 1 overnight.
• Annual interest rates (hypothetical):
  • EUR annual rate: 3%
  • USD annual rate: 5%
• Day-count and conversion assumptions:
  • Use 360-day year for the overnight fraction.
• We compute the annual differential:
  • Differential = EUR rate − USD rate = 3% − 5% = −2%.

Step-by-step

1. Convert the annual differential to an overnight fraction:
   • Overnight fraction = 1 / 360.
2. Convert differential to a one-day rate:
   • Overnight rate = (−2%) × (1/360) = −0.000055555…
3. Apply to notional value:
   • Notional = 100,000 EUR.
   • Overnight swap amount (in EUR) ≈ 100,000 × (−0.000055555…) = −5.5555 EUR.

Interpreting the result

• The negative sign corresponds to a swap charge for this hypothetical long EUR/USD scenario, because the USD side has the higher rate in our assumptions.
• Your account may show the result in USD, may net it differently, and may apply provider-specific markups or derived pricing. Those differences are part of why provider terms matter.

Limitations, risks, and failure modes

1) Provider terms can change the output

The real swap on a trading platform is determined by the provider’s contract rules. Even if the broad logic is “interest differential,” the actual posted swap can differ due to:

• internal pricing methodology,
• contract specifications (including lot definition and quoting conventions),
• how rollover days are handled (weekends/holidays).

2) Timing and day-count assumptions can be wrong

The example used a 360-day convention and a single overnight. In practice, the number of rollover days may differ, and platforms may apply different conventions. That can materially change the computed swap.

3) Market inputs are variable

The interest differential is not fixed. If rates move between trade entry and rollover, the realized swap will differ. A worked example based on hypothetical rates cannot predict future swap.

4) Execution and settlement uncertainty

Swap adjustments follow the platform’s trade lifecycle. If execution timing, partial fills, or account-specific settlement mechanics differ from the assumptions, the observed swap will not match the calculation.

Verification and next question to ask

To independently verify a swap outcome, you need three things from your own situation:

1. Your exact contract terms (lot size, rollover timing, and how the swap is calculated or posted).
2. The currency-direction (long base vs short base).
3. The relevant input values used on rollover day (rates or provider-derived values, plus any day-count and weekend handling).

A useful next question is: “For my exact instrument and platform, what is the posted swap formula or displayed swap rate, and how does it map to notional and rollover timing?”