A system and kit for assisting a subject in administering an injectable drug by use of an injection device having communication means to communicate data at least about sizes of doses expelled and a timestamp for when each dose was expelled. The system comprises a communication unit (210) adapted to communicate with the injection pen (100) to receive said dose data and comprising a display to present information and instructions to the subject. The system has a processor unit (220) comprising one or more processors and a memory storing a dose size calculation program adapted calculate a recommended dose size of drug to be injected. Responsive to a request to calculate a recommended dose size, the memory stores instructions that, when executed by the one or more processors, performs the initial step of prompting the user to perform a priming of the injection device before a calculation of a recommended dose size can be carried out.
