Late-life well-being often shows steep deteriorations, but the contributing factors are not well understood, in part because data about people’s final year of life are scarce. Here, we draw from and test theoretical perspectives that health-related vulnerabilities undermine the experience and skills older adults typically use to maintain well-being (Charles, 2010). To do so, we examined how various morbidity factors shape final-year well-being trajectories. We applied change score models to retrospective proxy-reports from the Socio-Economic Panel (N = 1,776; age at death = 19–101 years; 47% women) and covary for characteristics of the deceased and the bereaved proxy. Terminal decline in proxy-reported well-being amounted to 0.57 SD in less than a year, with larger individual differences at 3 months versus 12 months before death. Declines were reportedly steeper for those in poor health, need of care, not dying from sudden causes of death, dying with cancer, and not dying at home. People who entered their final year with preserved well-being and cognition experienced steeper final-year decrements. Morbidity factors conjointly accounted for less than 20% of variance, indicating that health decrements shape final-year well-being in multifaceted ways, but are not the be-all and the end-all of why well-being declines for some, but not for others. Unique effects of particular morbidity factors were modest, suggesting that prevailing multimorbidity makes the particular conditions in part interchangeable. Extending self-report data typically available until 1 year before death, our findings suggest that proxy-based results move our understanding of terminal well-being decline further.