Population ageing poses certain challenges for the countries concerned, particularly with regard to long-term healthcare. Looking after an elderly person with decreasing independence generates both public and private costs which add up to billions of euros every year. The objective of this analysis is to study the determinants of the willingness to pay (WTP) of informal carers for the assistance which they provide to elderly people aged 75 and over living at home, using the contingent valuation method. The data used are taken from the 2008 Handicap-Santé Aidants informels (HSA) (Health and Disability - Informal carers section) national survey. In them, questions are found on the amount carers would be prepared to pay to be relieved from one hour of assistance. A two-step model by Heckman was constructed to analyse both the factors linked to the reported amounts, and the reasons why certain carers did not wish to give an amount (protesting respondents). According to the results, characteristics such as the distance between the place where the person being cared for and the carer live and the deterioration of the mental health of the former show the need for recognition of informal carers through the declared values which are associated with them, as well as their need for relief, due to the burden which they bear sometimes for several years. The socio-economic context also plays an important role: the higher the income of the carer and the person being cared for, the higher the WTP amount. These elements may be useful to public policy-makers who are responsible for developing measures with the aim of both boosting the informal assistance provided to elderly people and relieving those providing it.