This research scrutinizes the extent to which long-term interest-rate conditions are stably associated with Indian equity returns. The examination uses NIFTY 50 price returns and the Indian 10-year government bond yield, with the former being observed from January 2012 to July 2026. Moreover, we note that the yield represents an endogenous market price. It is not an exogenous policy instrument. Hence, the association will be framed as a stable association investigation. Moreover, the research will also look into parameter stability. This does not involve analysis of policy-induced transmission. We employ an array of methodologies, namely two unit-root tests, several HAC-robust regressions, an ARDL(1,1) framework, Granger-causality assessments, a post-2020 interaction model, and rolling monthly coefficients. The full-sample yield coefficient is economically insignificant (−0.019, p = 0.969, R2 ≈ 0.00001), and there is no significant predictive content in either yield changes, lagged yields or Granger tests. Any hypothesis of parameter stability is rejected. The slope from 2012 to 2019 is +0.577 (p = 0.286). The slope from 2020 to 2022 is −2.600 (p = 0.048). The slope from 2020 to July 2026 is −1.678 (p = 0.077). The slope from 2023 to July 2026 reverts to +0.823 (p = 0.605). The post-2020 interaction is −2.255 (p = 0.039). On average, the yield-equity relationship is weak and concentrated in the pandemic-to-tightening transition, consistent with state-dependent pricing. The results warn against condensing rate sensitivity into a single full-sample coefficient, motivating regime-aware, higher-frequency identification.