The timescale at which ductile failure occurs in loaded glassy polymers can be successfullypredicted using the engineering approach presented in a previous publication.In this paper the influence of progressive physical ageing on the plastic deformationbehaviour of uPVC is characterised and incorporated in the existing approach. Withthe modification it is possible to quantitatively predict long-term failures which showa so-called endurance limit. The predictions are compared with failure data of uPVCspecimens which were subjected to constant or dynamic loads. In dynamic loadingconditions a second type of failure mode was observed: fatigue crack growth. A brief study on the influence of the applied stress signal shows that crack growth failure isnot expected to occur within experimentally reasonable timescales for constant loadingconditions.