Month-end rebalancing is the trading that investors do at the end of each month, some of it at the 4pm fix, to restore currency hedges and portfolio weights that the month’s price moves have disturbed.
Exemples
Example 17.5 (Two month-end flows)
Investors holding USD 2 trillion of American equities, hedged at 50%, sell trillion USD 40 billion forward after a 4% rise. A fund of USD 100 billion at 60/40, after the American part gained 5% and the European part lost 1%, must sell USD 1.44 billion of American assets and buy the same value of European ones.