  An efficient method for calculating inclusive conventional and prompt
atmospheric leptons fluxes is presented. The coupled cascade equations are
solved numerically by formulating them as matrix equation. The presented
approach is very flexible and allows the use of different hadronic interaction
models, realistic parametrizations of the primary cosmic-ray flux and the
Earth's atmosphere, and a detailed treatment of particle interactions and
decays. The power of the developed method is illustrated by calculating lepton
flux predictions for a number of different scenarios.
