Quantum key distribution (QKD) is the idea of using quantum systems to securely communicate a shared encryption key between two parties. In contrast to classical methods of encryption, QKD utilizes fundamental quantum properties such as superposition and entanglement to encode information in a way that guarantees security. Most QKD systems are based on sending photons in an optical fiber where the polarisation of the photons is the quantum property used to encode information. The different algorithms used to do this are referred to as QKD protocols. This thesis aimed to construct an educational tool to simulate simple QKD systems using four common QKD protocols, where the user can vary system parameters and study its effect on the results. Furthermore, the aim was to be able to produce simulation results that are accurate enough to provide a first approximation of how a real experimental setup would perform. The program was built in Python using the Qiskit library and all the desired features were implemented in a graphical interface. For one of the implemented protocols (BB84) the simulation results were compared to experimental data from a QKD experiment in Copenhagen, which indicated that the program is able to produce a useful first approximation of a real experimental setup. The program could be further improved by allowing for simulations of more complex systems.