This paper develops a quantitative model of bank failures to study how funding maturity and debt dilution shape balance-sheet dynamics and the timing of default. Empirically, banks approaching failure increase leverage, rely more heavily on time deposits, and experience compressing net interest margins and rising credit losses. Motivated by these patterns, the model features heterogeneous banks that choose between short- and long-maturity liabilities under limited commitment and capital regulation. Time deposits reduce rollover risk and smooth liquidity needs, but because equity can be rebuilt only through retained earnings, long-maturity funding creates incentives to dilute outstanding creditors through additional issuance. This debt-dilution channel amplifies fragility as fundamentals deteriorate, generating endogenous default and reproducing key pre-failure dynamics observed in the data. Overall, the results highlight liability-side incentives as a central driver of bank fragility.