We analyze the impact of the length of incomplete contracts on investment and surplus sharing. In the bilateral relationship explored, the seller controls the input and the buyer invests. With two‐part tariffs, the length of the contract is irrelevant: the surplus is maximal and goes to the seller. In linear contracts, the seller prefers the shortest contract and the buyer the longest one. Further, the commitment period concentrates the incentives, whereas afterwards there is rent extraction. The socially efficient contract is as short as possible; yet, long contracts can be promoted because of the surplus they allocate to the buyer.