Law 7 - The Duration of the Match
Source - FIFA.com
Periods of play
The match lasts two equal periods of 45 minutes, unless otherwise mutually agreed between the referee and the two teams. Any agreement to alter the duration of the periods of play (e.g. to reduce each half to 40 minutes because of insufficient light) must be made before the start of play and must comply with competition rules.
Players are entitled to an interval at half-time.
The half-time interval must not exceed 15 minutes.
Competition rules must state the duration of the half-time interval.
The duration of the half-time interval may be altered only with the consent of the referee.
Allowance for time lost
Allowance is made in either period for all time lost through:
- assessment of injury to players
- removal of injured players from the field of play for treatment
- wasting time
- any other cause
The allowance for time lost is at the discretion of the referee.
If a penalty kick has to be taken or retaken, the duration of either half is extended until the penalty kick is completed.
An abandoned match is replayed unless the competition rules provide otherwise.