It is not an offence to be in an offside position.
A player is in an offside position if:
any part of the head, body or feet is in the opponents’ half (excluding the halfway line) and
any part of the head, body or feet is nearer to the opponents’ goal line than both the ball and the second-last opponent
The hands and arms of all players, including the goalkeepers, are not considered. For the purposes of determining offside, the upper boundary of the arm is in line with the bottom of the armpit.
A player is not in an offside position if level with the:
second-last opponent or
last two opponents