A fully parameterized three-dimensional model with specific dimensions has been developed in ANSYS for an insulin injection pen used by diabetic persons. The insulin injection pen has a smart pen cap which hosts four electrodes used for the smart pen cap electrode capacitive measurement. The addition of the smart cap on top of the insulin injection pens is novel and essential for storing and transmitting injection dose and time data to help patients successfully manage their treatment. The simulations can be used to decide the number and exact shape of the electrodes, as well as to evaluate different misalignment and asymmetries of the electrode fabrication process or of the liquid misplacement. Using Maxwell 3D tool the electrode capacitance was numerically evaluated, which is necessary for sensing and ultimately for insulin dose precise detection. Experimental results have been provided using an AD7746 high-resolution sigma-delta capacitance-to-digital converter (CDC). Simulation and experimental results for the sense electrode capacitance, in the case of both smart pen cap and complete insulin injection pen + smart pen cap system, have been obtained, using two different configurations (1 vs 3 and 2 vs 2 respectively). Smart pen cap electrode capacitance variation for different insulin fill states has been numerically evaluated and the linear behavior of the injection has been proven.