Stage theories propose that individuals pass through different stages on their way toward behavior change. The present study examines stage-specific prediction patterns of social-cognitive variables (risk perception, outcome expectancies, perceived self-efficacy, action planning and social support) regarding transitions between the three stages of the Health Action Process Approach (HAPA; preintention, intention and action stage). In an online study (n = 494) on fruit and vegetable intake, social-cognitive variables and stages were assessed at baseline and stage transitions 4 weeks later. Transitions between the preintention, intention and action stage were predicted by social-cognitive variables using binary and multinomial logistic regression analyses. Stage-specific prediction patterns emerged for stage progression and stage regression. Outcome expectancies predicted progression from the preintention stage, whereas social support predicted progression to the action stage. Low levels of planning were associated with relapse to the preintention and the intention stage. Self-efficacy emerged as a universal predictor of stage transitions. Findings support not only the usefulness of the stage construct for describing health behavior change but also the validity of the HAPA variables as predictors of stage transitions. Stage-matched interventions targeting the variables identified as stage-specific predictors might support stage progression toward the goal behavior.