Various type of Instruments
When an investor keeps positions open overnight after 22:00 GMT, a swap is debited or credited in to trading account based on the positions type one is having. Swap charges are calculated based on the interest rate differential between two currencies of the pair and is calculated based on whether you have buy or sell position.
NOTE: As markets are closed on Saturday and Sunday, if investors keep positions open on Friday after 22.00 GMT, banks calculate the swap for 3-days.
An investor can directly see the swap charges in the instrument specification window of the trading platform.