Due to the large expansion in concrete projects and due to the importance of time and its direct impact on project cost, an essential need to estimate the hardened concrete strength within the first few hours of casting the concrete. In addition to that, it is known that in most concrete projects, casting of concrete is done in a consequence stages, so if the obtained hardened concrete strength is less than the target strength, then the time could be too late to take the necessary and right action. On the other side, if the obtained hardened concrete strength is more than target one then again it is uneconomical and time is done to save the wasted money in getting such a high unnecessary strength. Based on that, in this research the available methods of predicting hardened concrete strength at early stage were reviewed. One of these methods is developed and the effect of water cement ratio and cement dose on early strength estimation is discussed. Using non linear regression analysis, a theoretical model is established to estimate consolidated concrete strength at 7 and 28 days by knowing its strength after 6 h of its casting. Accelerating tests for early determination of concrete strength are used to generate expressions for prediction of hardened concrete strength as composite function of cement content and W/C ratio. By testing more than 200 cubes, the suggested theoretical model shows a good agreement with experimental results.