Premier League clubs can tweak their squads in January with the purchase and sale of players during the winter transfer window.
Windows were introduced as part of a compromise agreement with the European Commission about how the whole transfer system worked and how it could best preserve contractual stability for both the player and the club while allowing movement at prescribed times during the year - the summer and winter transfer windows in effect.
The winter transfer window usually opens on the first day of the New Year and closes at 11pm GMT on the last day of January. These dates may slightly vary from year to year.
If deadline day is a weekend or a bank holiday, there is flexibility to go into the next working day, which is normally until 5pm.