Despite mounting debt concerns, Chinese cities have aggressively expanded subway systems beyond their fiscal capacity. Why do local officials eagerly pursue financially risky infrastructure projects that often exceed their jurisdictions’ ability to repay? Using a panel dataset of 38 Chinese cities from 2015 to 2023, the analysis employs a two-way fixed effects model to examine how prefectural Party secretaries’ investment decisions are shaped by their expected remaining tenure—the time they anticipate serving in their current post, estimated from their career history and local political patterns. The findings reveal that Party secretaries with shorter expected tenures accumulate higher fiscal burdens on the Subway Debt Index—a measure of planned subway commitment relative to city fiscal capacity—reflecting an intertemporal asymmetry in which political credit crystallizes at project initiation while debt obligations transfer to successors. Conversely, those expecting longer tenures exercise greater fiscal restraint, as they may bear the financial risks that materialize during their own term. Robustness checks using mayors’ expected tenure yield consistent directional effects. The 2017–2018 central policy tightening substantially reduced aggregate debt accumulation, and COVID-19 disruptions attenuated the tenure-debt relationship, together demonstrating how institutional constraints and exogenous shocks interact with career incentives.