Over the past decade there has been significant progress in calculating muon stopping sites using first-principles methods such as density functional theory (DFT). However, such calculations are still only carried out by a relatively small number of research groups and are not yet a routine part of analysing a muon-spin spectroscopy (µSR) experiment. Here I introduce MuFinder , a program that facilitates the process of calculating muon sites by allowing these calculations to be run through a graphical user interface, with the aim of making this procedure more accessible to users who are not necessarily experts in electronic structure methods. I will demonstrate how muon site calculations can be carried out using MuFinder and then illustrate how they can enhance the interpretation of µSR experiments using examples from my research. First, I show how knowledge of the muon sites helps us to understand how the muon provides sensitivity to the unpaired spins in layers of the candidate quantum spin liquid material 1T-TaS2. In the second example, I show how DFT calculations of muon-stopping states provide evidence that the spontaneous local magnetic fields detected using muons in superconductors with time-reversal symmetry breaking (TRSB) are intrinsic to the TRSB superconducting state and not the result of a muon-induced perturbation .