[en] We have presented a new approach to obtain the cumulative solar proton event fluence distribution at a desired confidence level and for a given period of time. Compared to previous models, the main advantages of the current model are: it includes a broader proton energy range (> 1 to > 300 MeV); it includes more recent data; it is formulated with analytic expressions and is therefore simpler to update and work with; it is consistent with previous probabilistic models of worst case solar proton event fluences, and worst case peak fluxes, thus providing a more complete complement of tools for the spacecraft designer. (authors)