Objectives In response to concerns about the sustainability of health care systems that increasingly rely on informal care, we first investigate explanations of informal caregivers’ subjective well-being: primary stressors (care-receivers’ cognitive impairment, functional disability, and problem behavior), primary appraisal (hours of informal caregiving), and secondary appraisal (burden). Second, we investigate the extent that formal (professional home care) and informal support (from other caregivers/volunteers and from family/friends) alleviate well-being losses due to informal care provision. We modified the stress–appraisal model to explicitly include buffering effects of support. Method We analyzed 4,717 dyads of Dutch informal caregivers and their older care-receivers from the Older Persons and Informal Caregivers Survey Minimum DataSet with multilevel techniques. Results Caregivers’ subjective well-being was directly correlated with burden, hours of informal caregiving, and problem behavior of care-receivers. It was indirectly correlated with care-receivers’ cognitive impairment and functional disability. Formal and informal support weakened the positive relationship between primary stressors and caregiving hours. Discussion Modification of the stress–appraisal model appears useful as it identifies which sources of support buffer at which stages of the stress process. Findings suggest that cutbacks in formal/professional care may aggravate negative well-being outcomes of informal caregiving and compromise informal caregivers’ labor market participation.