Stage 1 Registered Report protocol submitted to PCI Registered Reports (v2; corrected secondary-data bias level to Level 4). Prior panel evidence on whether moving from paid employment into self-employment improves or harms well-being is mixed. We preregister a within-person fixed-effects analysis of the UK Household Longitudinal Study (Understanding Society) to provide an unbiased estimate of how transitions into self-employment relate to (a) subjective financial well-being and (b) psychological distress (GHQ-12), and whether any change persists or adapts over time, with preregistered moderators (necessity vs. opportunity entry; solo self-employment vs. employer; gender). Bias-control Level 4: the data exist and are accessible in principle via the UK Data Service, but the authors certify they have not accessed any part prior to in-principle acceptance. The analysis pipeline is written and validated on simulated data and frozen before data access.