The importance of informal care provided inside the household (co-residential care) is widely acknowledged in policy circles. However, the factors that determine the likelihood and scale of provision are not fully understood. A two-part model (2PM) is used to investigate both participation and levels of provision. Random effects dynamic panel specifications are employed. Results show that co-residential informal care competes with other time demanding activities, such as childcare and employment. Wealthier individuals are less likely to be caregivers, whereas wealthier households have a higher tendency towards caregiving. Evidence of both substitution and complementarity is found between formal and informal care. Informal care and health status are significantly related, with carers more likely to report worse General Health Questionnaire scores than non-carers. Finally, significant dynamic effects are observed with the continuance of the provision of informal care being more likely than the initiation of such activity, while heavy commitment in the past increases the hours provided in the current period.