The ideal family size in the UK is, on average, two children. However, there is a fertility gap, the difference between wanted and achieved family size, of around one in three children, which is largely caused by extended delays to reproduction. Standard quantitative methods used to identify what causes these delays have limitations, often relying on macro-level data which conveys little about individual needs, or applying longitudinal methods that produce outdated results because only once people have completed their reproductive years is it possible to infer which life-course factors led to later-age childbearing. This study is the first to overcome these challenges by applying a discrete choice experiment to reveal the barriers that people are facing right now. This innovative methodology allows the estimation of the relative importance of the barriers and the distance between them measured in months of reproductive delay. Among other things, the results show that for men and women, partner support was more important than finances or housing, although support means different things depending on the level of education with more educated women prioritizing hands-on fathers and household gender equality, whereas less-educated women strongly desired stable partnerships. Men favored partner readiness and neighborhood quality. These, and the other findings shown here, provide detailed insight into the contemporary causes of delayed fertility in the UK.