A large body of literature suggests that becoming a grandparent has beneficial consequences for subjective well-being, improved mental health, and happiness. These findings however are based on studies that compare grandparents to non-grandparents which is problematic because many unobserved characteristics are unaccounted for. This is especially important when studying self-reported measures of well-being given their subjective nature – people have different internal concepts about how happy they are. We tested whether becoming a first-time grandparent is associated with increased subjective well-being and found no such evidence across fifteen countries in Europe, nor when we replicated these tests in the UK, or in the USA. We used fixed effects models with longitudinal data which allow well-being to be compared, within the individual, before and after the grandparent event. This design means that any unobserved heterogeneity between people is controlled for. I will discuss what these null findings mean for social and evolutionary theories of grandparenting.