In the space of 20 minutes on the last Friday in June, the value of the U.S. dollar jumped 0.57 percent against its Canadian counterpart, the biggest move in a month. Within an hour, two-thirds of that gain had melted away.
The same pattern -- a sudden surge minutes before 4 p.m. in London on the last trading day of the month, followed by a quick reversal -- occurred 31 percent of the time across 14 currency pairs over two years, according to data compiled by Bloomberg. For the most frequently traded pairs, such as euro-dollar, it happened about half the time, the data show.
