Background: Health care systems aim to involve as much informal care as possible and dementia patients prefer to stay home as long as they can. In this context, perseverance time (Pt)—the period that the informal carer indicates to be able to maintain current care if the situation remains stable—is an important concept. Objective: The aim of this study was to introduce the concept Pt and validate it in a sample of informal carers of dementia patients living at home.