Despite the many benefits of exercising for both physiological and psychological health, almost half of the Australian population is insufficiently active. Using the self-determination theory, the transtheoretical model, self-efficacy and outcome expectancy theory as the literary framework, this study examined the predictors of long-term free-choice exercise adherence in a community sample. An online questionnaire battery was distributed to new gym members from the general community (N = 59) to measure their type of motivation, cognitive stage of change, level of self-efficacy for exercise and perceived outcome expectancy toward exercise, three times over a 12 week period. Results revealed that only stage of change was a successful predictor of exercise adherence. Further, transition between stages over the three collection times related to the trajectory of participant adherence over the 12 weeks. Findings in this study integrate recent work of community populations into the growing body of research focusing on the determinants of exercise. It is proposed that unexplained constructs exist in community populations that do not exist for specialised research populations and current theory may be insufficient in accounting for behavioural patterns outside those specialised populations.