Stage 1 Registered Report protocol submitted to PCI Registered Reports. 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). Data will be accessed only after in-principle acceptance; no analysis variables have been observed (secondary-data bias Level 5). This deposit is the Stage 1 manuscript file for peer review.