Associations between family size and offspring education depend on aspects of parental personality

•Parental personality has been associated with family size.•Personality may also influence trade-offs between offspring quantity and quality.•Neuroticism and openness modified correlations of family size and offspring education.

Personality traits have been associated with fertility rates, but little is known how parental personality is associated with trade-offs between family size and offspring outcomes. Using the Wisconsin Longitudinal Study (n = 5422 parents with 17,253 adult biological offspring), we examined whether parental personality traits assessed with the Five Factor Model (extraversion, neuroticism, agreeableness, conscientiousness, and openness to experience) modified associations between family size (measured as offspring number and birth order) and offspring education. Compared to low parental neuroticism, high parental neuroticism was associated with stronger trade-off between number of offspring and offspring educational achievement. High parental openness to experience, in turn, was associated with higher educational achievement of early-born offspring but not of later-born offspring. These personality-dependent differences in trade-offs between family size and offspring outcomes may help to explain why some personality dimensions are associated with low fertility rates.