Research rooted in the existentialist theory of the will to meaning has demonstrated that individuals who experience a sense of calling to their work realize personal well-being benefits. An assertion in the literature is that work may be understood as employed work or volunteer work. The calling research, however, has been limited to late-stage first age adults preparing for employment or second age adults currently employed. Calling among third age adults, post-employment and engaged in volunteer work, has not been examined thoroughly and is not well understood. In the US, the number of third age adults is growing by over 10,000 per day and by the year 2030 will have more than doubled since the census of 2000. The coming decades will see a significant need to address the well-being concerns of the nation’s aging population. The purpose of this quantitative, correlational study was to extend the understanding of the calling construct by examining the relationship between calling and eudaimonic well-being, and the potentially moderating effect of religiosity on that relationship, among third age adults in the volunteer domain. By means of an online survey, responses were collected from a nation-wide, purposive sample (N = 221) of age 65 or over adults (52% female) who were active volunteers. Multiple regression analyses revealed that upon controlling for gender, marital status, education, and income, calling, t(1) = 9.77, p < .001, and religiosity t(1) = 5.58, p < .001, were the only significant predictors of eudaimonic well-being. Moderated multiple regression analyses revealed that religiosity moderates the relationship of calling and eudaimonic well-being, but only at the aggregate, F(1,217) = 8.46, p = .004, R2 = .026, and highly-religious, F(1,217) = 10.146, p < .05, R2 = .031, levels of religiosity. The findings of this study extend the understanding of the calling construct beyond its previous parameters and provide a model of hope for practitioners engaged with third age adults. Future studies could more closely examine the relationship between calling and eudaimonic well-being in correlation with sources of calling, types of religious influence, or types of volunteer activities among third age adults.