Stages of Change lie at the heart of the TTM. Studies of change have found that people move through a series of stages when modifying behavior. While the time a person can stay in each stage is variable, the tasks required to move to the next stage are not. Certain principles and processes of change work best at each stage to reduce resistance, facilitate progress, and prevent relapse. Those principles include decisional balance, self-efficacy, and processes of change. Only a minority (usually less than 20%) of a population at risk is prepared to take action at any given time. Thus, action-oriented guidance mis-serves individuals in the early stages. Guidance based on the TTM results in increased participation in the change process because it appeals to the whole population rather than the minority ready to take action.

Surprisingly, none of the leading theories of therapy contained a core construct representing time. Traditionally, behavior change was often construed as an event, such as quitting smoking, drinking, or overeating. TTM recognizes change as a process that unfolds over time, involving progress through a series of stages.