CSMA/CA protocols such as IEEE 802.11b are considered to be attractive MAC protocols for wireless LANs. In this paper, we extend a saturation throughput model for the IEEE 802.11 Distributed Coordination Function (DCF) MAC protocol to finite loads. The analytical model can help in the optimization of the protocol parameters as well as leading to the performance modeling of multi-hop ad hoc networks. The model is verified using simulations, and it is shown that the model is extremely accurate.