External bonding of fiber reinforced polymer (FRP) sheets has been proven to be an effective method to strengthen and retrofit deteriorated or damage RC or PC structures. However, the long-term serviceability of such FRP-strengthened beams is still a concern due to lack of long-term performance data especially for prestressed FRP sheets. This study presents a manual method for predicting the short-term and time-dependent deflections for RC beams strengthened by prestressed or non-prestressed FRP sheets. The age-adjusted effective modulus method is used to model the creep behavior in concrete and the relaxation in FRP prestressing sheets. A tension-stiffening model is presented to evaluate the stiffness of the cracked section. The analytical values are compared to the results obtained from a finite element code, and to the experimental results from some existing papers. It is found that the analytical method is in a good agreement with finite element methods