Rising public expectations and health care costs along with demographic ageing raise questions about whether individuals should consider the drain on community resources when deciding whether to have expensive, life-extending medical interventions towards the end of their lifespan. All respondents (n = 208) in this novel, policy-capturing study were prepared to nominate an age along their life trajectory where they would likely decline a life-extending medical intervention indicating a "sense of limits" or "reasonableness" associated with the concept of a natural lifespan. The results showed that individuals altered end-of-life decisions in circumstances of higher opportunity cost and competing need but their propensity to do so was affected by their age, gender, and their expectations of medical progress. Other within-person factors (type of scarcity, treatment side effects, and health at diagnosis) affected the age one would decline a medical intervention in the face of a life threatening illness. Between-person predictors of this age included subjective life expectancy and attitude to health spending. The results suggest possibilities for building on this sense of reasonableness in public discussions of the opportunity cost of current health care resource allocation and by having physicians consider appropriate ways of presenting cost of treatment in end-of life contexts.