Why are swaps charged triple on Wednesday?

Although the Forex market operates continually 24 hours per day, positions are still accounted for on a daily basis and the end-of day time in Forex is 5:00 PM New York time.  This means that if you have any positions open at 5PM NY time, they need to be "rolled over" to the next trading day.

The settlement date of most Forex instruments is 2 days from the date that the position was closed.  If you close your position before 5 PM NY time on any given day, the settlement date will be 2 days out and this will be the date that the banks will physically deliver the currencies involved in the trade.

In the case of Wednesday, if you close your positions before 5PM the settlement date will be 2 days in the future, which is Friday.  However, if you hold your positions open past 5PM, the position is 'rolled over' to Thursday which will settle on the following Monday.  This is due to the fact that banks do not operate on Saturday or Sunday.

The result is that the daily rollover charge is applied to account for not only Wednesday, but Saturday and Sunday as well.