Self-consolidating concrete is a desirable achievement in reinforced concrete structures. This non-vibrating concrete has had a significant impact on the prestressed concrete industry because it increases productivity in the casting of durable prestressed or precast members without mechanical vibration. In the design of prestressed concrete structures, the immediate and time-dependent losses in tendon stresses are important. The main objective of this study is to investigate the losses in tendon stresses of indeterminate (continuous) post-tensioned unbonded beams consisting of two different types of concrete (high-strength self-consolidating concrete (HSSCC) and high-strength normal concrete (HSNC)). Six continuous, unbounded, post-tensioned I-beams in two groups were cast and monitored by electrical strain gauges for a duration of 60 d and the losses were measured. Results were compared with the Association of State Highway and Transportation Officials (Aashto) third and fourth edition methods, the Precast/Prestressed Concrete Institute (PCI) method and the Eurocode 2 model. It was found that the Aashto third edition, PCI and Eurocode 2 methods were conservative and the Aashto fourth edition method was non-conservative for estimating time-dependent losses in post-tensioned beams cast with high-strength concretes. The amount of experimental time-dependent losses in beams consisting of HSSCC was slightly lower than that of beams prepared using HSNC with almost the same concrete strength.