September 5, 2017
Equities in the US beginning with trading on September 5 will now settle in two days, not three. T + 2 begin for trades on Tuesday, September 5 -- the day after Labor Day. T+3 had been used since 1995 when the settlement cycle was shortened from T+5. The last trades to settle on a T+3 basis were those on Friday September 1.
A main reason for the change is risk reduction. The reasoning is that the fewer days for settlement, the less the risk. And the move to T+2 will align North America with other global markets that currently operate in T+2.