Resumen: The main goal of this research is to determine the link between happiness and individual subjective life expectancy (SLE) among Chilean senior citizens. We use data from the 2015 edition of the Chilean Social Protection Survey. Our sample consists of 1298 seniors: 700 aged 65–74, 421 aged 75–84, and 177 aged 85 and older. We provide a novel methodological approach that allows us to measure the relative contribution of happiness to SLE, by combining the Shapley–Owen–Shorrocks decomposition with contrasts of marginal linear predictions of the equality of the means by groups. Results reveal that happiness is the most important determinant of seniors’ SLE, and the effect is stronger the older the people are. Addressing varying levels of happiness is important because both happiness and unhappiness have a significant impact. In an ageing population, social agents should consider that these variables (happiness and SLE) are related to engagement in healthy lifestyles. If prevention programs integrated this interaction, welfare systems could save scarce resources. Therefore, governments should foster happiness to support active ageing. Idioma: Inglés DOI: 10.3390/math9172050 Año: 2021 Publicado en: Mathematics 9, 17 (2021), 2050 ISSN: 2227-7390 Factor impacto JCR: 2.592 (2021) Categ. JCR: MATHEMATICS rank: 21 / 333 = 0.063 (2021) - Q1 - T1 Factor impacto CITESCORE: 2.9 - Engineering (Q2) - Mathematics (Q2) - Computer Science (Q3)