In low-fertility contexts, previous research shows a persistent gap between actual and desired or intended family size. Understanding discrepancies between fertility ideals, intentions, and behaviour is highly relevant, as this provides invaluable insights into the age-specific mechanisms that govern the realisation (or non-realisation) of individuals’ intended or desired family size. Using novel data of eleven European countries from the Generations and Gender Survey, collected during and after the COVID-19 pandemic (2020-2023), we compared ideal, intended, and actual fertility for women aged 18-49. We calculated two fertility gaps among women in different age-groups and, for the first time, analysed these gaps as dependent variables using linear regression models. We examined how socio-demographic factors are linked to the intended number of children among women aged 18-29, the fertility gap to intentions among women aged 30-39, and the fertility gap to ideals among women aged 40-49. The results indicate the intended family size for ages 18-29 ranges from 1.82 (Finland) to 2.47 (Moldova). The gap between women’s mean ideal and actual family size (40-49) ranges from 0.42 to 0.63 across countries. The multivariable analyses reveal similar country patterns: Religiosity particularly matters for intended fertility early in the reproductive life course, while education plays a role in the primary phase of family formation. Moreover, all models confirm the high relevance of partnership status. Since fertility intentions are significantly higher than period fertility, this suggests that the early 2020s fertility decline could have been driven by uncertainty and – as a consequence – a postponement of childbirth.