Age structure and its dynamics are critical in understanding the impact of population growth on a country’s growth prospects. Using state-level data from India, we show that the pace of demographic transition varies across states, and that these differences are likely to be exacerbated over the period 2011-2026. We show that the so-called BIMARU states (Bihar, Madhya Pradesh, Rajasthan, and Uttar Pradesh) are likely to see a continuing increase in the share of the working-age population in total population. The BIMARU states are expected to contribute 58% of the increase in India’s working-age population. The BIMARU states have traditionally been the slow-growing states and have performed poorly on different accounts of social and physical infrastructure. Whether India can turn demographic dividend into a boon or whether the dividend will become a bane will critically depend on the ability of the BIMARU states to exploit the bulge in the working-age population.