Cultural Momentum, Demographic Divergence, and Population Prospects in India, 2100: Son Preference as a Structural Driver of Fertility and Long-Term Projections

Standard cohort-component projection models for India omit one of the most durable behavioural drivers of fertility: son preference operating through Differential Stopping Behaviour (DSB). This paper addresses that gap by introducing son preference as an explicit stratification dimension alongside education and urban-rural residence extending the Vienna School’s multi-dimensional demographic framework to include gender norms as a structural modifier of fertility. Using a relational Gompertz framework estimated from a 300-cell state-by-residence-by-son-preference-category-by-NFHS-round panel, we find that son preference raises TFR by 15.4 per cent net of all socioeconomic controls and shifts the fertility schedule toward older ages. A 10 per cent permanent reduction in DSB-driven fertility from 2021 yields approximately 50–60 million fewer people across 15 major states by 2100; an SSP2-style counterfactual places the full demographic cost at 426 million. Shift-share decomposition reveals that in Uttar Pradesh and Bihar, cultural momentum defined as cumulative population divergence from the sustained gap between observed and structurally expected fertility operates alongside demographic momentum as a binding constraint. These results suggest that projection models conditioned only on development covariates may understate long-run population size in high-preference states.