If you are talking about otc and pinks you need to know when it comes out on the Daily List: http://www.otcbb.com/asp/dailylist_detail.asp?d=01/20/2012&mkt_ctg=ALL Once you see it there, it is official and it will happen the next trading day. Companies sometimes will release a proposed reverse split in a PRE14 - there is usually time before they come out with the official announcement (it could be weeks or months). But once it is on the Daily List it means it is official - the change will happen the next trading day. We post the reverse splits on this board: http://investorshub.advfn.com/boards/board.aspx?board_id=3017