This paper presents a dynamic model of firm financing where firms use financial slack to reduce rent extraction by financiers with bargaining power. Financing is lumpy because it is optimal to bargain infrequently. Moreover, firms may finance ‘early’ before exhausting internal funds to bargain when their outside options are better. Financing rents are thus endogenous to firms' dynamic financing strategy. Firms with good financing alternatives raise financing early to reduce rents, whereas firms lacking such alternatives raise financing after exhausting funds to avoid paying endogenously large rents too frequently. Investment irreversibility increases financing rents – and disproportionately for unproductive firms.