According to international banking practice, forex transactions are executed after 2 trade days (T+2). For example, the deal is traded on Monday. The execution date will be Wednesday.
Monday: overnight interest for 1 day that holding order from Monday through Tuesday, and then execution date is Wednesday through Thursday. Therefore, the client will be paid/charged overnight interest for 1 day.
Tuesday: overnight interest for 1 day that holding order from Tuesday through Wednesday, and then execution date is Thursday through Friday. Therefore, the client will be paid/charged overnight interest for 1 day.
Wednesday: overnight interest for 3 days that holding order from Wednesday to Thursday, and then the execution date is Friday through Monday. Therefore, the client will be paid/charged overnight interest for 3 days.
Thursday: overnight interest for 1 day that holding order from Thursday through Friday, and then the execution date is Monday through Tuesday. Therefore, the client will be paid/charged overnight interest for 1 day.
Friday: overnight interest for 1 day that holding order from Friday through next Monday, and then the execution date is Tuesday through Wednesday. Therefore, the client will be paid/charged overnight interest for 1 day.