CONTEXT: Americans express a strong preference for participating in decisions regarding their medical care, yet they are often unable to participate in decision-making regarding their end-of-life care. OBJECTIVE: To examine determinants of end-of-life planning; including, the effect of an individual's ageing and dying process, health status and socio-economic and racial/ethnic background. METHODS: US observational cohort study, using data from the Health and Retirement Study (1992 - 2014) including 37,494 individuals. Random-effects logistic regression analysis was used to examine the relationship between the presence of a living will and a range of individual time-varying characteristics, including time to death, and several time-invariant characteristics. RESULTS: End-of-life planning depends on several patient characteristics and circumstances, with socio-economic and racial/ethnic background having the largest effects. The probability of having a living will rises sharply late in life, as we would expect, and is further modified by the patient's proximity to death. The dying process, exerts a stronger influence on end-of-life planning than does the aging. CONCLUSIONS: Understanding differences that increase end-of-life planning is important to incentivize patients' participation. Advance planning should be encouraged and accessible to people of all ages as it is inevitable for the provision of patient-centered and cost-effective care.