Reproductive Inflation: Devaluation of the Biological Window and a Slack-Time Theory

Reproductive inflation as the devaluation of the biological window: the same years of fertility yield a shrinking capacity to achieve a desired family size, because life-coursepreconditions (education, partnership, housing, income, readiness) are met later while the biological deadline moves comparatively little. We give definitions from five perspectives (demographic, economic, clinical, epidemiological, ethical) and an integrated formal definition. The framework rests on five quantities: the biological deadline D, the lead time L, the slack S = D − L, the squeezed share Σ = Pr(L > D), and the reproductive purchasing power of the window, RPP = (D − a 0 )/(L − a 0 ). The inflation rate π = Δ ln(L − a 0 ) − Δ ln(D − a 0 ) decomposes into a socio-behavioural component (which precondition is met last) and a biological-technological component (health and assisted reproduction). The theory is consistent with microsimulation evidence that postponing first birth by 3–4 years lowers completed fertility by only 0.1–0.2 children, with assisted reproductive technology (ART) offsetting at most about 10% of that decline, while the share of couples eligible for infertility treatment risessubstantially. Its central prediction follows: reproductive inflation shows up first in effort, risk and medicalisation, and only secondarily in the number of births. Treatment cost (cost-to-baby) is treated as one channel that extends the deadline. Reproductive intelligence (Hudziak, 2026) is introduced as an individual-level moderator through misperception of the deadline and a “hidden squeezed share”. Ten falsifiable hypotheses with explicit refutation criteria are stated.The framework is descriptive and makes no claim about reproductive choices or a societal “loss of reproductive potential”