Abstract
This study centers on retirement planning achievement, examining its impact mechanism on older adults' mental health and its boundary conditions. Drawing on self-determination theory (SDT) and conservation of resources (COR) theory, we tested a parallel mediation and a moderated mediation model using data from an online survey with 900 Chinese retirees aged 55-74. Structural equation modelling revealed that retirement planning achievement directly and positively predicted mental health, and indirectly through three pathways: greater active social participation, higher retirement enjoyment, and reduced retirement loss. Furthermore, retirement adjustment exhibited dual, and opposing, moderating effects on the direct path: low retirement loss, as a psychological resource, significantly amplified the positive impact of planning achievement (a resource gain spiral), whereas high retirement enjoyment attenuated its effect (a ceiling effect). Income-group analysis revealed that both the parallel mediation and moderated mediation models were fully supported in the average-income group, but effects were non-significant for the insufficient-income group and weakened in the sufficient-income group. These findings suggest that retirement planning achievement represents a key pathway to promoting mental health in later life, but its benefits are constrained by psychological resources and socioeconomic status. The "achievement dividend" is greatest among well-adjusted retirees in the average-income group, highlighting the heterogeneity in retirement adjustment and providing evidence for targeted, equitable ageing-support policies.