If the client holds the position over Wednesday night (for FX currency pairs) and Friday night (for Indices), the triple swap rate will be charged for that position. The reason for this is spot contracts have a two-day settlement period. Thus, the triple charge is accounted as a settlement for the weekend swap which can not be charged during weekends due to the market being closed. 

For example, a spot Forex contract that occurred on Monday settles on Wednesday, a trade that occurred on Tuesday settles on Thursday, a trade that occurred on Wednesday settles on Friday, however, a trade that occurred on Thursday settles on the following Monday. In this example, the trade that occurred on Thursday rolled through the weekend. Since the banks are closed on Saturday and Sunday, triple rollover interest is applied to positions held open at 5 pm New York time on Wednesday, as this time marks the beginning of the new 24-hour trading day (Thursday).

You should note that swap rates can be negative or positive, depending on the instrument traded and the prevailing interest rates at that time. The detailed information can be accessed from MetaTrader 4 or MetaTrader 5 platform under the 'Specifications'.