Let’s say that the EUR/USD is trading at 1.2500, the USD federal funds rate is 2.5%, and
the
European Central Bank’s interest rate is 3.25%. If you open a short position (sell) on
the
EUR/USD for 1 lot, you are essentially selling €100,000, borrowing it at an interest
rate of
3.25%. By selling EUR/USD, you’re buying USD, which earns a 2.5% interest rate. The
interest
rate differential is 0.75.
Now let’s say your broker charges a 0.25% mark-up for the swap. Since the interest rate
of
the currency you are selling (EUR) is higher than that of the currency you are buying
(USD),
you add the mark-up in the formula. If you add this to the 0.75% interest rate
differential,
the total interest the broker charges is 1.00%.
For this example, we use a 365-day year but some brokers will typically use 360 days.
Others
will use both 365 days and 360 days depending on the instrument being traded. Using the
formula:
In this case, you are selling the EUR and its interest rate is higher than the USD one,
therefore, the USD 3.42 is deducted from your account when your EUR/USD position rolls
over
to the next day.