A swap/rollover fee is charged when you keep a position open overnight. A forex swap is the interest rate differential between the two currencies of the pair you are trading, and it is calculated according to whether your position is long or short. The Range Markets Swap Calculator can be used to determine what your swap fee will be for holding a trade open overnight. To calculate swap fee, select the instrument you are trading, your account currency and trade size, and click ‘Calculate’.
For forex, the Swap Calculator works as follows:
Swap = (Pip Value * Swap Rate * Number of Nights) / 10