Stage-matched interventions can only be more effective than “one-size-fits-all” interventions if they target participants' specific needs. Therefore, individuals must be allocated to a stage that truly reflects their mindsets. Various criteria for stage allocation exist. This study's objective was to demonstrate the impact of different classification criteria on stage allocation, and which criterion yields the best reflection of individuals' mindsets. The sample consists of 569 internet users. Physical activity, intention to change, and four stages of change (Non-Intender, Intender, Maintaining Actor, and Changing Actor) were assessed. Staging was based on two criteria: individual criteria and externally imposed criteria (30 min of physical activity on at least 4 days of the week). Hypotheses were tested by multivariate analyses and validity tests. As predicted, the different criteria affected stage allocation, and staging based on the individual criterion seemed to reflect individuals' intention to change and behavior better than staging based on the external standard.