An image forming apparatus and a controlling method thereof are provided. The image forming apparatus includes a communication interface unit which is connected to a server where on-line output quota information set for each user is stored, a storage unit which stores off-line output quota information received from the server, a controller which, when a job command is input in an on-line state where communication with the server is available, determines whether to perform a job based on on-line output quota information stored in the server, and when the job command is input in an off-line state where communication with the server is cut off, determines whether to perform a job based on the off-line output quota information stored in the storage unit, and an image forming unit which, when job performance is determined by the controller, performs an image forming job corresponding to the job command.