Agent-Based Modelling of Family Behaviour and the Postponement of Childbearing

The paper addresses the problem of separating the temporary postponement of births from the permanent reduction in their number, with reference to low fertility in Europe and Russia. The limits of aggregate tools – the period total fertility rate, which conflates tempo and quantum, and the cohort-component projection, which relies on exogenous trajectories – are outlined, and the shift to agent-based modelling of family formation is justified. The paper is conceived as a review-and-methodology study: no original computational experiments are carried out; its subject is the rationale for the change of instrument, the architecture of the model and the programme of its empirical verification. A multilevel model is proposed, comprising individuals, partnerships, households and regions, in which the birth decision follows a logistic rule with a separate probability of birth and of deferral. European evidence (EU total fertility rate of 1.34 in 2024, mean age at first birth of 29.9 years, a cross-country range from 1.01 to 1.72) is compared with Russian evidence (a rise in the age at first birth from 22.65 to 26.02 years, the dominant negative contribution of first births to the 2015–2023 decline). Drawing on domestic agent-based models, requirements for validation and interval reporting are formulated. A set of family-policy scenarios is proposed that distinguishes measures accelerating the timing of births from those raising the completed number of children, together with an estimate of the budgetary cost of the outcome.