The Transtheoretical Model (TTM, the “stage model”) can guide development of programs to increase Medicare beneficiaries' readiness to make informed health plan choices. In this study, TTM staging algorithms were developed to assess readiness to engage in three types of informed choice: (1) learning about the Medicare program; (2) learning about Medicare health maintenance organizations (HMOs); and (3) reviewing different plan options. Stage of change based on all three algorithms is related to knowledge about the Medicare program and information-seeking. Findings provide evidence for the construct validity of the stage measures and for the applicability of the TTM to informed choice among beneficiaries.