Abstract: The authors present a simple and accurate stochastic model for the steady-state throughput of the slow but steady variant of TCP NewReno. The model describes the relations between TCP NewReno throughput and round trip time, rate of packet loss and retransmission timeout value. This work motivated by the recent measurement studies indicates that there are more than half of TCP streams which use TCP NewReno instead of Reno fast recovery with a non SACK receiver. The proposed model builds upon the approach proposed by Padhye for TCP Reno throughput modeling but extends it by capturing the effect of the fast recovery algorithm and taking into consideration the slow start phase after timeout expiration. The measurement studies suggest that these behaviors are important from a modeling perspective. And the proposed model is formulated by using a new loss model instead of foregoing loss model used by Padhye, which can better represent the loss scenarios encountered by TCP on the Internet. Validation by NS2 simulator shows that using Padhyes model to estimate TCP NewReno throughput may introduce significant error while the proposed model is able to accurately predict the steady-state throughput for TCP NewReno over a wide range of network conditions.