Access to housing constitutes a growing global problem, with a particular impact on young people and vulnerable groups. The sustained increase in housing prices, together with stagnant incomes, has generated an excessive financial burden for lower-income households. Spain’s new Law 12/2023 on the right to housing incorporates the concept of affordability, defined as a level of housing expenditure that does not exceed 30 per cent of household income. The study shows that this definition has substantial limitations. The literature on affordability, its indicators, and measurement methods is reviewed, and a redefinition of the term is proposed for a more effective housing policy. The proposal integrates vertical equity, minimum residual incomes, and territorial differences.