Premier League clubs are permitted to conduct the purchase and sale of players during the winter and summer transfer windows.
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 alternative was to bring football in line with most other industries where contracts were not enforceable or liable for appropriate compensation, i.e. notice periods being served and players moving at will. The football authorities across Europe felt this would fatally undermine the footballing economy and remove the incentive for clubs to invest in developing players.
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.
The summer transfer window usually opens on June 10 and closes at 11pm BST on the final day of August. 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.