Demographic Momentum — Why the Problem Persists

A critical misunderstanding in the political debate: falling fertility does not immediately slow population growth. Demographic momentum — continued growth driven by a large young-adult cohort already in the childbearing age — means that UP and Bihar will continue growing in absolute terms for decades even as their TFR approaches replacement [@cite_pib_demography_2040].

Over one-third of India's total population increase between 2011 and 2036 will come from these two states alone, while all five southern states see their population share declining.

This momentum is the mechanism that makes the delimitation problem acute: even with Bihar projected to reach replacement fertility by 2039 and UP by approximately 2025–2027, the population advantage accumulated over 50+ years of higher fertility takes another 30–40 years to dissipate demographically. The 2027, 2037, and 2047 censuses — the basis for the next three delimitation rounds — all fall within the window of maximum divergence.